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Page 1: Genetics. 2 ReynoldsUnwrapped.comReynoldsUnwrapped.com offers FANTASTIC, inexpensive daily email subscriptions, where you can receive a HILARIOUS new

Genetics

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Genetics

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Experimental genetics began in an abbey garden

The modern science of genetics began in the 1860s when a monk named Gregor Mandel deduced the fundamental principles of genetics by breeding garden peas.

Mendel lived and worked in an abbey in Austria.

Strongly influenced by his study of physics, mathematics, and chemistry at the University of Vienna, his research was both experimentally and mathematically rigorous, and these qualities were largely responsible for his success.

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Mendel In a paper published in 1866,

Mendel correctly argued that parents pass on to their offspring discrete hereditary factors.

He stressed that these hereditary factors (today called genes) retained their individuality generation after generation.

In other words genes are like marbles of different colors: just as marbles retain their colors permanently and do not blend, no matter how they are mixed, genes permanently retain their identities.

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Mendel

Mendel probably chose to study garden peas because he was familiar with them from his rural upbringing, they were easy to grow, and they came in many readily distinguishable varieties.

Perhaps most importantly, Mendel was able to exercise strict control over pea plant matings.

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Mendel

The petals of the pea flower almost completely enclose the reproductive organs.

Consequently, pea plants usually self-fertilize in nature. That is, pollen grains land on the egg of the same flower.

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Mendel

Mendel could ensure self-fertilization by covering a flower with a small bag so that no pollen from another plant could reach the egg.

When he wanted cross-fertilization (fertilization of one plant by pollen from a different plant), he used a particular method so that he could be sure of the heritage of the new plants.

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Mendel

Mendel worked with his plants until he was sure he had true breeding varieties-- that is, varieties for which self fertilization produced offspring all identical to the parent. In other words, a “pure-bred” plant).

For instance, he identified a purple flowered variety that produced offspring plants that all had purple flowers.

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Hybridization

Now Mendel was ready to ask what would happen when he crossed his different true breeding varieties with each other.

For example, what offspring would result if plants with purple flowers and plants with white flowers were cross fertilized?

In the language of the plant and animal breeders and geneticists, the offspring of two different varieties are called hybrids, and the cross-fertilization itself is referred to as hybridization, or simply a cross.

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Hybridization

The true breeding parental plants are called the P generation and their hybrid offspring are the F1 generation.

The offspring of F1 plants are known as the F2 generation.

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Genotype and Phenotype Genotype means the type of genes a person

has, or their genetic make-up. Genes, the units of heredity that control the specific

characteristics of an individual, are arranged in a linear fashion along the chromosomes.

Alleles are a pair of genes on a pair of chromosomes that affect the same trait. For instance, both chromosomes have an allele for eye color, both have an allele for skin color, etc.

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HEREDITARY PHYSICAL CHARACTERISTICS

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HEREDITARY PHYSICAL CHARACTERISTICS

Those genes that affect the same trait are called alleles.

A dominant allele is given a capital letter, and a recessive allele is given the same letter in lower case.

For instance, having an earlobe that is unattached to the face is a dominant trait, so we can call it E.

An attached earlobe would then be called e.

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Alleles

Alleles occur in pairs; just as one pair of each type of chromosome is inherited from each parent, so too each pair of alleles are inherited from each parent.

The allele which is traditionally indicated by an uppercase (capital) letter is the dominant trait.

The allele which is traditionally indicated by a lowercase (small) letter is the recessive trait.

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Homozygous

If a sperm cell has e and the egg cell has e, the offspring must have ee.

That is called homozygous (pure) recessive. That means the person would have an attached

earlobe. If a sperm cell has E and the egg cell has E, the

offspring must have EE. This is called homozygous (pure) dominant.

That means the person would have an unattached earlobe.

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Homozygous

The term for “pure” is homo. It refers to something being the same.

In the old days, you had to shake up milk because the cream would rise to the top. Nowadays, people want less fat, so the cream is removed before you get it; this is called homogenized milk.

A homogenized mixture is one that is the same throughout, and requires no periodic mixing.

Therefore, when the allele pairs are either EE or ee, they are homozygous.

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Heterozygous

The opposite of homo is “hetero”, so an allele pair that is “Ee” is heterozygous.

If one of the sex cells has E and the other sex cell has e, what will the offspring have? Ee.

What type of earlobe will they have? Unattached. Why? Because the dominant trait is stronger, so if it is present at all, it will manifest.

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Phenotype

The physical appearance of a person is called the phenotype.

A person with Ee will therefore be called a heterozygous genotype, with an unattached earlobe phenotype.

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Sample Problems

What earlobe alleles will a person have who is homozygous recessive? ee

What earlobe alleles will a person have who is homozygous dominant? EE

What earlobe alleles will a person have who is heterozygous? Ee

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Figuring the Odds

If one of the parents is homozygous dominant (EE), the chances of their having a child with unattached earlobes is 100 %, because this parent has only a dominant allele (E) to pass on to the offspring.

On the other hand, if both parents are homozygous recessive (ee), there is a 100% chance that each of their children will have attached earlobes.

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Figuring the Odds

However, if both parents are heterozygous, then what are the chances that their child will have unattached or attached earlobes?

To solve a problem of this type, it is customary first make a table (Punnet Square) of the genotype of the parents and their possible gametes.

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Punnet Square

E e

E EE Ee

e Ee ee

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Figuring the Odds That means that when Harry meets Sally,

their child has a 25% chance (1:3) of being ee, and 25% chance of being EE, and 50% chance (1:1) of being Ee.

But that’s just the genotype. What about the phenotype (what will the child look like)?

There is a 75% chance (3:1) of having an unattached earlobe (Ee or EE).

There is a 25% chance (1:3) of having an attached earlobes (ee).

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Sample Test Questions

In crossing a heterozygous parent and a homozygous recessive parent, what is the percent chances that an offspring will receive a dominant allele?

Answer = 50%

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Sample Test Questions

What is the ratio of the phenotype for crossing two heterozygous parents for ear lobe attachment?

What is the ratio of the genotype for crossing two heterozygous parents for ear lobe attachment?

3:1

1:2:1

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Sample Test Questions

Free earlobes (E) are dominant over attached earlobes (e).

If two people with homozygous attached earlobes mate, what will be the phenotype of their offspring?

All attached earlobes

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Sample Test Questions

What is the ratio for crossing a heterozygous parent for ear lobe attachment and a homozygous recessive parent:

1:1

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Sample Test Questions

In crossing two heterozygous parents, what are the chances (in percent) for a pure recessive offspring?

25%

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For calculating eye color, let’s say the father has brown eyes (BB) and the mother has blue eyes (bb).

Use the Punnet Square to calculate the odds of what the child will look like. The father’s alleles are written in the vertical column and the mother’s on the horizontal.

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When we fill in the squares, we see that all of the children will be heterozygous (Bb) genotype. What color eyes will the babies all have? Brown. Therefore, the phenotype of all the children will be “brown-eyed”.

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What if the father had brown eyes but his genotype was Bb instead of BB and they had 4 children?

Two of their children would have the genotype Bb (heterozygous for brown eyes), and two of their children would have the genotype bb (homozygous for blue eyes). Therefore, there is a 50% chance that each child would have the phenotype of brown eyes and 50% chance that each child will have the phenotype of blue eyes.

b

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What if both parents were heterozygous? One child would have the genotype BB, two would have the

genotype Bb, and one would have the genotype bb. That means that three out of four children would have brown eyes and one would have blue eyes. Therefore, there is a 75% chance their child will have brown eyes and 25% chance they will have blue eyes.

Another way to write this is that there is a 3:1 ratio of brown eyed to blue eyed children.

That would describe the phenotype (appearance), but the genotype would be written as

1:2:1

B

b

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PERSONAL PHENOTYPE ANALYSIS

Everyone clasp your hands together and hold them in the air: which thumb is on top? “Thumb crossing” is a genetic phenotype.

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PERSONAL PHENOTYPE ANALYSIS HANDEDNESS: Do you write with your right or left hand? Left handedness is

recessive. MID-DIGITAL HAIR: do you have hair on the middle segment of your fingers and

toes? HITCHHIKER’S THUMB: Make a fist with your thumb extended. Is there almost a 90°

angel between the first two joints of your thumb? It is a recessive trait. THE LENGTH OF THE INDEX FINGER in comparison to your ring finger is influenced

by your sex. A short index finger is dominant in males and recessive in females. COLOR BLINDNESS: Look through the color-blindness testing books on the

demonstration table. Can you distinguish the numbers and patterns on each page? About 8% of American males and 0.4% females are recessive for red and green color blindness.

PTC TASTERS: If you place a PTC test paper on your tongue for a minute, to some people it will taste bitter. Others do not taste anything. People who taste bitterness also tend to dislike broccoli and Brussels sprouts.

SODIUM BENZOATE: This is a food preservative; taste this paper in the same way. Does it taste salty, sweet, sour, bitter, or not at all to you?

NUTRASWEET: Does this taste sweet or bitter to you?

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MAKE A BABY INSTRUCTIONS

Now everyone is going to make a baby. Ready? Set? GO! (Just kidding) Use the Make a Baby Handout. Each of you should take a penny and work in pairs; it doesn’t matter if

your partner is the opposite sex. There is a Data Table towards the end of the handout that you can record the characteristics of your baby. Record your names as parents on this data sheet. Then determine the sex of the child by flipping the coin. Give your child a name and record it. Every time you flip the coin, heads means a dominant trait, so write it down as a capital letter. Tails means it is a recessive trait, so write it down as a small letter. Each parent donates one gene (one letter) so the child has two letters. Then check the instructions to see what the baby’s letter combination represents.

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Getting Started

1. FACE SHAPE Flip your coin; if it’s heads, write down a capital

R, because you have donated a dominant characteristic to your baby. If it was tails, write down a small “r” because the gene you gave your baby is recessive. Then your partner flips the coin for face shape. If the two flips result in Rr, or rr, then your baby has a round face. If the two flips were RR, your baby has a square face. Record this in your data table.

Complete the rest of the traits to see what your baby looks like!

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REVIEW OF GENETICS

Our nucleus contains 46 chromosomes (23 pairs). A chromosome is a double-stranded string of DNA. Stretched out, it is six feet long!

DNA is made of a string of molecules called nucleic acids. There are only 4 different nucleic acids: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).

Each A, T, G, or C on one strand of DNA is paired to its counterpart on the other strand of DNA.

Adenine (A) only pairs with Thymine (T), and Guanine (G) only pairs with Cytosine (C).

When they pair up, they are called base pairs. There are about 250 million base pairs of nucleic acids on one chromosome!

The double strand of DNA looks like a ladder. It is then twisted into a shape called a helix.

Therefore, DNA is a double-stranded helix.

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When the body needs a particular protein, the double-stranded DNA helix unwinds, just in the segment that contains the nucleic acid sequence (called a GENE) for that protein. The DNA strand that is copied is called the sense strand (or + strand), and the other strand is called the antisense strand (or – strand).

The gene is copied in the nucleus and the copy is taken to the cytoplasm, then taken to a ribosome, which reads the nucleic acid sequence.

Every three nucleic acids code for one particular amino acid. These amino acids are then linked in the proper order in the ribosome, and the protein is made.

When a person has a genetic defect, it is because the nucleic acids are not in the exact right order. There may be one nucleic acid substituted for another. There may be a new nucleic acid inserted. There may be a nucleic acid deleted. These things will displace the rest of the nucleic acid sequence. Sometimes, just one amino acid in the wrong order will cause death in a person before they are born.

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A gene is a particular sequence of nucleic acids on the DNA strand of the chromosome. The function of the genes on the DNA is to tell RNA to tell a ribosome how to make a particular protein. Proteins carry out most of the functions of the body.

TRANSCRIPTION is the process of DNA creates the RNA strand in the nucleus. The type of RNA it makes is called mRNA (messenger RNA). The gene on the DNA is like my hand. I want to duplicate my hand, so I make a clay mold of it. The clay mold is the messenger RNA molecule. This occurs in the nucleus. The mRNA then exits the nucleus through a pore and

goes to the cytoplasm.

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TRANSLATION is the process of mRNA is read by a ribosome, telling the ribosome what order to put the amino acids in. The amino acids become the protein. Therefore, translation is characterized by PROTEIN SYNTHESIS. This occurs in the cytoplasm. During translation, the mRNA (clay mold of my

hand) has already left the nucleus and is now in the cytoplasm. The RNA presents its “hand imprint” to the ribosome. The ribosome fills the hand imprint with “plaster” to make a positive cast, or a duplicate of the original gene.

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When the ribosome reads the copy of the gene (the nucleic acid sequence) that was made in the cytoplasm, every group of three nucleic acids is called a CODON. Each codon codes for one amino acid.

For example, if the first three nucleic acids are G, C, T, when you check that code in a manual, you find that means the first amino acid is Alanine. If the next three nucleic acids are C, C, G, that codes for Proline. Therefore, the ribosome links alanine to proline, and so on, until the entire amino acid sequence is finished.

This new protein is placed in an envelope for protection, and dumped into the endoplasmic reticulum. During its journey in the RER and then in the Golgi complex, protective molecular groups are placed around the delicate ends and side groups of the protein. After that, it is ready to start functioning.

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TRANSCRIPTION VIDEO TRANSCRIPTION WEBSITE

TRANSLATION VIDEO TRANSLATION WEBSITE

DECODING A GENE

DNA KIT PROJECT (Handout: Do page one now)

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Amino Acids build proteinsBuilding blocks of protein, containing an aminogroup and a carboxyl groupAmino acid structure: central C; amino group,acid group, and variable group

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a) AMINO ACIDS are MONOMERS (building blocks) of protein. They are tiny carbon molecules, made of just a carbon atom and a few other atoms.

There are only 22 standard types of amino acids in the human body (20 of them are involved in making proteins). Nine of these are essential amino acids, meaning that we have to get them in the diet. We can synthesize the others.

Amino acids are like beads on a necklace. Each bead is an amino acid, and the whole necklace is the protein. A bunch of the same types of necklaces (proteins) woven together makes up our tissues.

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Amino Acids

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Essential NonessentialHistidine AlanineLeucine ArginineIsoleucine AsparagineLysine Aspartic acidMethionine CysteinePhenylalanine Glutamic acidThreonine GlutamineTryptophan GlycineValine Ornithine

Proline

Selenocysteine

Serine

Tyrosine

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Mutations of Genes Mutation – change in the nucleotide base

sequence of a genome; rare Not all mutations change the phenotype

(appearance) Two classes of mutations

1. Base substitution eg point mutation

GTTCAAG - (normal) ATTCAAG - mutant (abnormal)

Silent mutation No change in amino acid sequence

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Mutations of Genes

Missense mutation New amino acid

ALA-PHE-LEU-TRY-STOP PHE-PHE-LEU-TRY-STOP

Non-sense mutation – a stop codon is inserted into protein sequence Truncated protein ALA-PHE-STOP-TRY-STOP

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Mutations

2. Frameshift mutation Insertion or deletion of one or more bases Original sequence: ATG CCA GGT AAG

Insertion: ATT GCC AGG TAA G Deletion: ATC CAG GTA AG_

If it happens at the end of a gene it may not be as bad

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Figure 7.20

Effects of Mutation

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Figure 7.9

Genetic Code

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DNA Handout: do pages 3-4 now Missense mutation eg. sickle cell

results in a codon that codes for a different amino acid. The resulting protein may be nonfunctional

Nonsense mutation eg Cystic fibrosis Stop codon is inserted, truncated protein

Frameshift insertion eg. Tay-Sachs disease Frame shift deletion CCR5

CCR5 is our cell membrane receptor that the HIV virus uses to attack. People with this genetic mutation are immune to many strains of the AIDS virus.

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Causes of mutations

Spontaneous mutations Happens during replication

More often in prokaryotes than eukaryotes.

Eukaryotes have better repair mechanisms.

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Mutagens

Radiation Ionizing radiation (x-rays) – induces breaks

in chromosomes Nonionizing radiation (UV light) – induces

thymine dimers Chemical Mutagens

Nucleotide analogs – disrupt DNA and RNA replication and cause point mutations Eg. 5-bromouracil pairs with guanine Caffeine not a strong mutagen – but it does

effect fetal development Alkylating agents- used for cancer treatment

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Figure 7.24

DNA Repair

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Figure 7.24

DNA Repair

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Radiation gigantism from the Fukushima disaster 

 http://www.lightlybraisedturnip.com/giant-squid-in-california/?fb_action_ids=10202951473416673&fb_action_types=og.likes&fb_source=aggregation&fb_aggregation_id=288381481237582

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Identifying Mutants, Mutagens, and Carcinogens

DNA DAMAGE VIDEO TUMOR GROWTH VIDEO Mutants – descendents of cell that does not

successfully repair a mutation Wild types – mutant cells normally found in

nature Methods to recognize mutants

Positive selection Survival of the fittest

Negative (indirect) selection selective removal of rare alleles that are deleterious.

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Genetic Recombination and Transfer

Recombination and transfer of genes occurs during exchange of DNA segments with those of another DNA segment

Recombinants – cells with DNA molecules that contain new nucleotide sequences

Vertical gene transfer – organisms replicate their genomes and provide copies to descendants

Horizontal gene transfer – donor contributes part of genome to recipient; three types Transformation Transduction Bacterial Conjugation

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Transformation Experiments

The transforming agent in the experiment was DNA; became the evidence that DNA is genetic material

Cells that take up DNA are competent.

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Figure 7.29

Griffith’s Transformation Experiment67

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Transduction

Transduction is the process by which DNA is transferred from one bacterium to another by a virus.

When bacteriophages (viruses that infect bacteria) infect a bacterial cell, their normal mode of reproduction is to harness the replication machinery of the host bacterial cell to make numerous virions, or complete viral particles, including the viral DNA or RNA and the protein coat.

Transduction explains how antibiotic drugs become ineffective due to the transfer of resistant genes between bacteria.

In addition, transduction experiments attempt to cure diseases such as Muscular Dystrophy.

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Figure 7.30

Generalized Transduction69

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Figure 7.31

Bacterial Conjugation70

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Figure 7.31

Bacterial Conjugation

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VIDEOS

CELL SIGNALS VIDEO (13 mins) STEM CELLS VIDEO

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French police on hunt for serial rapist stumped by identical twin suspects

Police are holding both brothers while they run extensive genetic tests to try to distinguish between the two. The complicated tests could cost more than $1 million.

The environment can change our DNA too. We all build up mutations in our DNA over time. Our DNA also changes in response to things like sunlight or the food we eat. 

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These changes are pretty rare. Everyone has about 100 new mutations in their DNA. Sounds like a lot but spread out over 3 billion base pairs, that is quite a needle in a haystack.

Also, all of the changes aren't in all of your cells -- not all of your cells have the same DNA sequence! If a DNA mistake happens late in our development, then only a few cells will have that mutation. If a mistake happens early, then more cells will have the DNA change but still not all of them.

The differences between identical twins increase as they age, because environmentally triggered changes accumulate. 

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Why do identical twins have different fingerprints?

While you were growing inside of your mother, you touched the amniotic sac.

When you touched it during weeks 6-13, the patterns of your fingerprints were changed.

This is why identical twins have different fingerprints.

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GENETIC DISORDERS

1. Chromosome Disorders 2. Sex Chromosomal Disorders 3. Dominant Disorders (only one dominate

allele needs to be present) 4. Homozygous Recessive Disorders

(both parents must have rr alleles) 5. Incompletely Dominant Traits 6. Sex-Linked Traits 7. Sex-Influenced Traits

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Down Syndrome

Down syndrome is also called trisomy 21 because the person’s chromosome number 21 has three chromosomes joined together instead of just two.

The chances of a woman having a Down syndrome child increase rapidly with age, starting at about age 40.

The frequency of Down syndrome is 1/ 800 births for mothers under 40 years of age, but women over 40 are 10 times more likely to have a Down syndrome child.

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Down Syndrome

Characteristics of Down syndrome include a short stature; an eyelid fold; stubby fingers; a wide gap between the first and second toes; a large, fissured tongue; a round head; a palm crease (the so-called simian line), and mental retardation, which can sometimes be severe.

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Down Syndrome

Their personalities are usually cheerful, good-natured, and pleasant throughout their lives.

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Down Syndrome

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Amniocentesis

Removing fluid and cells from the amniotic sac surrounding the fetus, followed by karyotyping can detect a Down syndrome child.

Scientists have located genes most likely responsible for the increased tendency toward leukemia, cataracts, accelerated rate of aging, and mental retardation.

One day it might be possible to control the expression of that gene even before birth so that at least this symptom of Down syndrome does not appear.

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Amniocentesis

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Cri du Chat Syndrome (“cat’s cry”) Cri du Chat Syndrome (“cat’s cry”) This is caused by one missing segment of

chromosome 5 and occurs in 1/ 50,000 live births. An infant with this syndrome has a moon face, small head, and a cry that sounds like the meow of a cat because of a malformed larynx. An older child has an eyelid fold and misshapen ears that are placed low on the head. Se vere mental retardation becomes evident as the child ma tures.

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Cri Du Chat Syndrome85

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Sex Chromosomal Disorders

All of the cells in our body have all of our chromosomes in the nucleus except for the egg and the sperm.

Each of these has all of our chromosomes in the nucleus, except there is only one of the two sex chromosomes.

Since women are XX, all of her egg cells are X, but since males are XY, a sperm can bear an X or a Y.

Therefore, the sex of the newborn child is determined by the father.

If a Y- bearing sperm fertilizes the egg, then the XY combination results in a male.

On the other hand, if an X-bearing sperm fertilizes the egg, the XX combination results in a female.

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Chromosomal Disorders

All factors being equal, there is a 50% chance of having a girl or a boy.

If a couple has 10 children and they are all boys, what is the chance that an eleventh child is going to be a boy?

Interestingly, the death rate among males is higher than for females.

By age 85, there are twice as many females as males.

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Jacob syndrome

occurs in 1/ 1,000 births. These XYY (an extra male chromosome) males

are usually taller than average, suffer from persistent acne, and tend to have speech and reading problems.

At one time, it was suggested that these men were likely to be criminally aggressive, but it has since been shown that the incidence of such behavior among them may be no greater than among XY males.

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Jacob Syndrome: XYY91

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Klinefelter syndrome

occurs in 1/ 1,500 births. These males with XXY (an extra female

chromosome) and they are sterile. They are males with some female

characteristics. The testes are underdeveloped, they have

some breast development, and there is no facial hair.

They are usually slow to learn but not mentally retarded.

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Klinefelter syndrome

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Klinefelter syndrome: XXY94

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Triple-X syndrome

occurs in 1/ 1,500 births. These are females with an extra female

chromosome: XXX. You might think they are especially feminine,

but this is not the case. Most have no physical abnormalities except

that they may have learning disabilities, menstrual irregularities, including early onset of menopause.

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Triple-X syndrome96

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Turner syndrome

occurs in 1/ 6,000 births. The individual is XO, meaning one of the sex

chromosomes is missing. These are females and have a short, broad

chest, and webbed neck. The ovaries and uterus are nonfunctional.

Turner females do not undergo puberty or menstruate, and there is a lack of breast development.

They are usually of normal intelligence and can lead fairly normal lives, but they are infertile even if they receive hormone supplements.

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Turner’s Syndrome

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Turner syndrome: XO99

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Dominant Disorders: Neurofibromatosis Used to be known as Elephant Man disease, this is one

of the most common genetic disorders. It affects roughly 1/ 3,000 people. It is seen equally in every racial and ethnic group

throughout the world. At birth or later, the affected individual may have six or

more “coffee with milk” colored spots (known as cafe-au-lait) on the skin.

Such spots may increase in size and number and may get darker.

Small benign tumors (lumps) called neurofibromas may occur under the skin or in various organs.

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Neurofibromatosis102

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Neurofibromatosis

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Neurofibromatosis

In most cases, symptoms are mild, and patients live a normal life.

In some cases, however, the effects are severe. Skeletal deformities, including a large head, are

seen, and eye and ear tumors can lead to blindness and hearing loss.

Many children with neurofibromatosis have learning disabilities and are hyperactive.

The abnormal gene is on chromosome 17.

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Dominant Disorders

Huntington Disease This affects 1/ 20,000 people. It is a dominant neurological disorder that leads to

progressive de generation of brain cells, which causes severe muscle spasms and personality disorders.

Most people appear normal until they are of middle age and have already had children who might also be stricken.

There is no effective treat ment, and death often comes ten to fifteen years after the onset of symptoms.

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Huntington’s Disease106

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Homozygous Recessive Disorders: Tay - Sachs disease

This disease usually occurs among Jewish people. At first, it is not apparent that a baby has Tay-Sachs

disease. However, development begins to slow down between

four months and eight months of age, and neurological impairment and psychomotor difficulties then become apparent.

The child gradually becomes blind and helpless, develops uncontrollable seizures, and eventually becomes paralyzed.

There is no treatment or cure for Tay- Sachs disease, and most affected individuals die by the age of three or four.

It is caused by a genetic enzyme deficiency.

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Tay - Sachs disease108

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Cystic Fibrosis This is the most common lethal genetic

disease among Caucasians in the United States.

About 1 in 20 Caucasians is a carrier, and about 1/ 2,500 births have the disorder.

In these children, the mucus in the bronchial tubes is particularly thick and interferes with breathing, and the lungs get infected frequently.

New treatments have raised the average life expectancy to 28 years of age.

The cystic fibrosis gene is located on chromosome 7.

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Cystic Fibrosis110

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Phenylketonuria (PKU)

This occurs in 1 / 5,000 births, so it is not as frequent as the disorders previously discussed, however, PKU is tested for in routine blood screenings of all newborns in the United States.

This is the disease that offspring of first cousins are more likely to get.

PKU people lack an enzyme that is needed to break down an amino acid (phenylalanine), and so the amino acid accumulates in the urine.

These people have to have a special diet that does not contain that amino acid.

If they get too much of it, they will get neurological problems and mental retardation.

That’s why nutrition labels have to warn when they contain phenylalanine.

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PKU112

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Incompletely Dominant Traits

Incomplete dominance is exhibited when there is an intermediate phenotype.

These people can be carriers of a disorder without being sick themselves.

Their children may have the disorder, or they also may be carriers.

When they are carriers, they are said to have the “trait” of the disorder, but not the disease.

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Sickle-Cell Disease

This is an incompletely dominant disorder. In persons with sickle-cell disease, the red blood cells aren’t

round disks like normal red blood cells; they are irregular. In fact, many are sickle shaped, like a banana with points

on both ends. The red blood cells do not carry oxygen well, and they get

stuck in arteries also. Therefore, people with this disease suffer from poor circulation, anemia, poor resistance to infection, internal bleeding, pain in the abdomen and joints, and damage to internal organs.

SICKLE CELL VIDEO

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Sickle-Cell Disease

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Incompletely Dominant Traits

Sickle-Cell Disease In malaria-infested Africa, infants with sickle-cell disease

die (they got a bad chromosome from both parents), but infants with sickle-cell trait (they got a bad chromosome from only one parent) actually have better resistance to malaria than a normal human being. The malaria parasite normally reproduces inside red blood cells. But a red blood cell of a sickle-cell trait infant kills the parasite.

Therefore, the only people who survive well in Africa are those with sickle cell trait. That’s why about 60% of the population in malaria-infested regions of Africa has sickle cell trait. Unfortunately, 25% of their offspring can get the sickle cell disease.

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Malaria

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Sex-Linked Traits

Traits controlled by alleles on the sex chromosomes are said to be sex-linked; an allele that is only on the X chromosome is X-linked, and an allele that is only on the Y chromosome is Y-linked.

Most sex-linked alleles are on the X chromosome since it is larger.

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X-Linked Disorders

X-linked conditions can be dominant or recessive, but most known are recessive.

More males than females have the trait. If a male has an X-linked condition, his

daughters are often carriers, so her male children are also likely to have the condition.

All of the following disorders are sex-linked.

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Male Pattern baldness

From a gene that is inherited from the mother.

For you guys, if your mother’s father was bald, you are more likely to be bald.

It doesn’t matter if your father is bald or if his father is bald.

You get the baldness gene from your mother’s father.

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X-linked Recessive Disorders

Three well-known X-linked recessive disorders (more common in males than females) are color blindness, muscular dystrophy, and hemophilia.

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Color Blindness

In the human eye, there are three different types of cone cells (remember, they sense color vision).

These different types are sensitive to either the color red, green, or blue.

The gene for the red and green cells is on the X chromosome.

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COLOR BLINDNESS TEST

About 8% of Caucasian men have red-green color blindness.

Opticians have special charts by which they detect those who are color blind.

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Muscular Dystrophy

As you can tell by the name, this disease is characterized by a wasting away of the muscles.

The most common form is X-linked and occurs in about 1/ 3,600 male births.

Symptoms, such as waddling gait, toe walking, frequent falls, and difficulty in rising, may appear as soon as the child starts to walk.

Muscle weakness progresses to the point where they need a wheelchair.

Death usually occurs by age 20; therefore, affected males are rarely fathers.

The disease is from a carrier mother to carrier daughter.

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Muscular Dystrophy126

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Hemophilia

About 1/10,000 males is a hemophiliac. It is due to the absence of a clotting factor. It is called the bleeder’s disease because the

blood does not clot. Every time they get a bruise, they have to have

either a blood transfusion or an injection of a clotting protein, which they keep in their refrigerator since they need it so often.

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X-Linked Disorders

In the early 1900’s, hemophilia was prevalent among the royal families of Europe, and all of the af fected males could trace their ancestry to Queen Victoria of England.

Of her 26 grandchildren, five grandsons had hemophilia and four granddaughters were carriers.

Because none of Queen Victoria’s ancestors or relatives were affected, it seems that the faulty allele she carried arose by mutation either in Victoria or in one of her parents.

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Hemophilia

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Her carrier daughters, Alice and Beatrice, introduced the gene into the ruling houses of Russia and Spain, respectively. Alexis, the last heir to the Russian throne before the Russian Revolution, was a hemophiliac. There are no he mophiliacs in the present British royal family because Victoria’s eldest son, King Edward VII, did not receive the gene and therefore could not pass it on to any of his descendants.

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Sex-Influenced Traits

The length of the index finger is sex-influenced.

In females, an index finger longer than the fourth finger (ring finger) is dominant.

In males, an index finger longer than the fourth finger seems to be recessive.

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Stem Cell Research

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Stem Cell Research

Some human illnesses, such as diabetes type 1, Alzheimer disease, and Parkinson disease, are clearly due to a loss of specialized cells. In diabetes type 1, there is a loss of insulin secreting cells in the pancreas, and in Alzheimer disease and Parkinson's disease there is a loss of brain cells. Specific types of cells are needed to cure these conditions.

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Stem Cell Research

Stem cells are cells that continuously divide to produce new cells that go on to become specialized cells. The bone marrow of adults and the umbilical cord of incidents contain stem cells for each type of blood cell in the body. It is relatively easy to retrieve blood stem cells from either of these sources. Researchers report that they have injected blood stem cells into the heart and liver only to find that they became cardiac cells and liver cells respectively!

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Stem Cell Research

The skin, gastrointestinal lining, and the brain also have stem cells, but the technology to retrieve them has not been perfected. Also, it has not been possible to change adult stem cells into a fully developed specific type of cell outside the body. If the technique is perfected, it might be possible to change a brain stem cell and to the type of cell needed by a Parkinson patient.

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Stem Cell Research

Today, young, relatively infertile couples seek assistance in achieving pregnancy and having children. During in vitro fertilization, several eggs and sperm are placed in laboratory glass, where fertilization occurs in development begins. A physician places two or three embryos in the woman's uterus for further development, but may hold back some encased bees fail to take hold. Embryos that are never used remain frozen indefinitely unless they are made available to researchers.

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Stem Cell Research

Each cell of an embryo is called an embryonic stem cell because it can become any kind of specialized cell in the body.

Researchers have already used non-human embryonic cells to create supplies of nonhuman specialized cells.

Therefore, they think the same will hold true with human embryonic stem cells.

If so, medicine would undergo an advancement of enormous proportions.

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Stem Cell Research

Even so, there is a down side. What about the embryos that had been forced to

give up the chance of becoming an adult in order to extend the health span of those already living? Would this be ethical?

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Stem Cell Research

In Great Britain, researchers can work with embryos that are 14 days or younger because embryos usually implant in the uterus around day 14. However, some people will leave that all human beings are equal, and ought not to be harmed or considered to be less than human on the basis of age or size or stage of development or condition of dependency. They believe that embryos should not be used as a means to an end, even good ends, such as a cure for diseases or to save another human life.

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Stem Cell Research

President George W. Bush agreed and signed an executive order that forbids the use of federal funds for the purpose of creating new cell lines derived from embryos in United States. The order does not affect any embryonic stem cell lines previously established nor any work with adult stem cells. Nevertheless, some researchers have left the United States to work in countries where stem cell research is freely allowed without governmental restrictions.

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Stem Cell Research

Stem cell research is a bioethical dilemma. Some say that to think in dualistic terms is not helpful; it isn't that an embryo is a human being or is not a human being, it's that a fully developed human being comes about gradually. For instance, what would you do if there was a fire in a fertility clinic and you were faced with the choice of saving a five-year-old girl or a tray of 10 embryos? Which would you choose? Some people also believe that stem cell research is ethical, but that humans should not be cloned.

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Stem Cell Research

Should researchers have access to embryonic stem cells or only adult stem cells? What is your reasoning?

Do you believe that while it is ethical to do research with embryonic stem cells to cure human illnesses, it is not ethical to clone humans? What is your reasoning?

Some researchers are mixing nonhuman and with human embryonic stem cells in order to study developmental differences. Is this ethical?

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 You can get a complete gene map of your unborn child -- but should you?

http://fxn.ws/OsO6tY

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Genetic Testing for Cancer Genes

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Genetic Testing for Cancer Genes

Several genetic tests are now available to detect certain cancer genes. If Winn and test positive for a particular type of defective gene, they have an increased risk for early onset breast and ovarian cancer. If an individual tests positive for a different type of gene, they are at greater risk for the development of colon cancer. Other genetic tests exist for rare cancers as well.

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Genetic Testing for Cancer Genes

Advocates for genetic testing say that it can alert those who test positive for these mutated genes to undergo more frequent mammograms or colonoscopies. Early detection of cancer clearly offers the best chance for successful treatment. Others feel that genetic testing is unnecessary because nothing can presently be done to prevent the disease. Perhaps it is enough for those who have a family history of cancer to schedule more frequent checkups beginning at a younger age.

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Genetic Testing for Cancer Genes

People opposed to genetic testing worried that a woman with a defective gene for breast cancer might make the unnecessary decision to have a radical mastectomy. In a study of 177 patients who underwent gene testing for susceptibility to colon cancer, less than 20% received any counseling before the test. Moreover, physicians misinterpreted the test results in nearly one third of the cases.

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Genetic Testing for Cancer Genes

It's possible, too, that people who test negative for a particular genetic VK Chin may believe that they are not at risk for cancer. This might encourage them not to have routine cancer screening.

Regular testing and avoiding known causes of cancer such as smoking, a high fat diet, or too much sunlight, are important for everyone.

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Genetic Testing for Cancer Genes

Should everyone be aware that genetic testing for certain cancers is a possibility, or should such testing the confined to a research setting?

If genetic testing for cancer were offered to you, would you take advantage of it? Why or why not?

Our protective measures to avoid cancer more important than testing? Explain.

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Choosing Gender

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Choosing Gender

You may feel that it is ethically wrong to choose which particular embryo can continue to develop following in vitro fertilization.

But what about choosing whether an X-bearing or Y-bearing sperm should fertilize the egg?

As you know, the sex of a child depends upon whether an X-bearing sperm or a Y-bearing sperm enters the eighth.

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Choosing Gender

A new technique has been developed that can separate each type of sperm. First, the sperm are dosed with a chemical. The X-chromosome has slightly more DNA than the Y-chromosome, so it takes up more die. When a laser beam shines on the sperm, the ex-bearing sperm shine a little more brightly. A machine sorts the sperm into two groups on this basis. The results are not perfect. Following artificial insemination, there is about an 85% success rate for a girl in about a 65% rate for a boy.

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Choosing Gender

Some might believe that this is the simplest way to make sure they have a healthy child if the mother is a carrier of an X-linked genetic disorder such as hemophilia or muscular dystrophy. Previously, a pregnant woman with these concerns had to wait for the results of an amniocentesis test and then decide whether or not to abort the pregnancy if it was a boy. Is it better to increase the chances of a girl to begin with? Or, do you believe that gender selection is not acceptable for any reason?

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Choosing Gender

Even if it does not lead to a society with far more members of one sex than another, there could be a problem. Once you separate reproduction from the sex act, it might open the door to genetically designing children in the future. On the other hand, is it acceptable to bring a child into the world with a genetic disorder that may cause an early death or a lifelong disability? Would it be better to select sperm for girl, who at worst would be a carrier like her mother?

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Choosing Gender Do you think it is acceptable to choose the gender of a

baby? Even if it requires artificial insemination at a clinic? Why or why not?

Do you see any difference between choosing gender or choosing embryos free of a genetic disease for reproduction purposes?

If selecting sperm is less expensive than selecting embryos, should women who are carriers of X-linked genetic disorders he encouraged to use this method of producing children who are free of the disease?

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Designer Children

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Designer Children

Human beings have always attempted to influence the characteristics of their children. For example, couples have attempted to determine the sex of their children for centuries through a variety of methods. Amniocentesis has allowed us to test fetuses for chromosomal abnormalities and debilitating developmental defects before birth. Modern genetic testing technology enables parents to directly select children bearing desired traits, even at the very earliest stages of development.

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Designer Children

Recently, a couple selected an embryo to cause, as a newborn, the individual could save the life of his sister.

The couple, Jack and Lisa Nash, had a daughter with Fanconi's anemia, a rare inherited disorder in which affected persons cannot properly repair DNA damage that results from certain toxins.

The disease primarily afflicts the bone marrow, and therefore results in a reduction of all types of blood cells.

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Designer Children

Anemia occurs, due to a deficiency of red blood cells.

Patients are also at high risk of infection, because of low white blood cell numbers, and of leukemia, because white blood cells cannot properly repair any damage to their DNA.

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Designer Children

Fanconi's anemia may be treated by a traditional bone marrow transplant, or by an adult stem cell transplant, preferably from a parent or a sibling, because the risk of rejection is lower. Adult stem cells are almost always the preferred treatment option, because stem cells are hardier and much less likely to be rejected in a bone marrow transplant. The umbilical cord of a newborn is a rich source of adult stem cells for all types of blood cells.

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Designer Children

The selection of an embryo on the basis of genes is accomplished by extracting a sample of the DNA, determining its sequence, and comparing it with known sequences for diseases. In this case, doctors examined the DNA of embryos to see if they had the gene in question, that the newborn would be healthy, and also would be able to benefit his sister. The parents underwent in vitro fertilization, and the 15 resulting embryos were screened to see if they were both free of the inherited disease in a match for their daughter.

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Designer Children

Two embryos met these requirements, but only one implanted in the uterus and it developed into a healthy baby boy. Adult stem cells were harvested from the umbilical cord of the newborn and were successfully used to treat his sister's anemia. The physician who performed the genetic screening stated that he has received numerous inquiries about performing the procedure for other couples with diseased children

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Designer Children

This case, and other related cases, has raised a number of ethical issues surrounding prenatal selection of children based on genetic traits.

While the AMA insists that selection based on traits not related to the disease is unethical, the AMA's share made an exception for this case, because the child was selected for medical reasons.

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Designer Children

Still, some people believe that it is dangerous to bear children for the purpose of curing others, and that it should be compared with a new form of biological slavery.

Others think that, soon, children will be selected for less altruistic reasons, such as for their height, physical prowess, or intellectual abilities.

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Designer Children

In general, do you think it is ethical to have children to cure medically related conditions, regardless of how fertilization occurs? If not, do you agree with the AMA that this case is an acceptable exception?

Because the brother was created as a treatment for his sister's disease, do you believe that there is a moral obligation to provide him with compensation?

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Designer Children

Would embryonic stem cells, to ride from Anna boarded penis and cultured in the laboratory, be an acceptable substitute?

Would you willingly donate sperm or eggs for in vitro fertilization to produce a healthy child for a couple who could not have won because of the risk of an inherited disease, such as Fanconi's anemia?

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Designer Children

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Designer Children

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Designer Children

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Designer Children

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Designer Children

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Reproductive and Therapeutic Cloning

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Reproductive and Therapeutic Cloning

Reproductive cloning and therapeutic cloning are done for different purposes. In reproductive cloning, the desired end is an individual that is genetically identical to the original individual. At one time, it was thought that the cloning of adult animals would be impossible because investigators found it difficult to have the nucleus of an adult cell start over, even when it was placed in an egg without a nucleus.

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Reproductive and Therapeutic Cloning

In March 1997, Scottish investigators announced they had cloned a sheep called Dolly.

How was their procedure different from all the others that had been attempted?

Unlike other attempts, the donor cells were starved for the cell's nucleus was placed in in a period starving the donor cells caused them to stop dividing and go into a resting stage, and this made the nuclei receptive to cytoplasmic signals for initiation of development.

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Reproductive and Therapeutic Cloning

By now, and it is common practice to clone all sorts of farm animals that have desirable traits and even to clone the rare animals that might otherwise become extinct.

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Reproductive and Therapeutic Cloning

In the United States, no federal funds can be used on experiments to clone human beings. Cloning is wasteful-- even in the case of Dolly, out of 29 clones, only one was successful. Also, there is concern that cloned animals may not be healthy. Dolly was euthanized in 2003 because she was suffering from lung cancer and crippling arthritis. She had lived only half the normal lifespan for her species of Sheikh.

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Reproductive and Therapeutic Cloning

In therapeutic cloning, the desired end is not an individual; rather, it is mature cells of various cell types.

The purpose of therapeutic cloning is to learn more about how specialization of cells occurs and to provide cells and tissues that could be used to treat human illnesses such as diabetes, spinal cord injuries, and Parkinson disease.

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Reproductive and Therapeutic Cloning

There are two possible ways to carry out therapeutic cloning. The first way is to use the exact same procedure as reproductive cloning, except embryonic cells are separated and each one is subjected to treatment that causes it to develop into a particular type of cell such as red blood cells, muscle cells, or nerve cells. Some have ethical concerns about this type of therapeutic cloning, which is still very experimental, because if the embryo were allowed to continue development, it would become an individual.

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Reproductive and Therapeutic Cloning

The second way to carry out therapeutic cloning is to use adult stem cells.

Stem cells are found in many organs of the adults body; for example, the skin has stem cells that constantly divide and produce new skin cells.

The bone marrow has stem cells that produce new blood cells as does the umbilical cord of newborns.

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Reproductive and Therapeutic Cloning

It has already been possible to use stem cells from the brain to regenerate nerve tissue for the treatment of Parkinson's disease.

However, the goal is to develop techniques that would allow scientists to turn any adult stem cell into any type of specialized cell.

Many investigators are engaged in this endeavor. In order to do this, scientists need to know how to control gene expression.

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