intro to genetics

Chapter 11 and 14 Genetics 2010 1

Intro to Genetics

Chapter 11.1-11.3

p. 306-322

Key terms



Review?Heredity: What is a gene?

is a segment of DNA that is located in a chromosome and that codes for a specific trait

Crossing over: How does it contribute to the physical differences between siblings?

exchange of genetic material between homologous chromosomes genetic recombination

THINK ABOUT IT What is an inheritance?

It is something we each receive from our parents—a contribution that determines our blood type, the color of our hair, and so much more.

What kind of inheritance makes a person’s face round or hair curly

Where does an organism get its unique characteristics

An individual’s characteristics are determined by factors that are passed from one parental generation to the next.

The delivery of characteristics from parent to offspring is called heredity.

The scientific study of heredity, known as genetics, is the key to understanding what makes each organism unique

4Chapter 11 and 14 Genetics 2010


leucism• This alligator is one of 18 white alligators discovered

southwest of New Orleans in 1987 by a fisherman. • How is he different from alligators you have seen?• It is not a different species and it is not albino. • Albinos have off-white or yellowish skin and colorless

irises or look pink• This alligator is more rare than one that would be an

albino.

http://sptimes.com/2005/12/15/images/large/WK_0_wk15gatr2_229802_1215.jpg


Need to know!!1. Describe how Mendel was able to control his

pea plants were pollinated.

2. Describe the steps in Mendel's experiments on true-breeding garden peas.

3. Distinguish between dominant and recessive traits.

4. State two laws of heredity that were developed from Mendel’s work

5. Describe how Mendel's results can be explained by scientific knowledge of genes and chromosomes


Mendel’s Legacy

• Genetics is the field of biology devoted to understanding how characteristics or traits are transmitted from parents to offspring. Genetics was founded with the work of Gregor Johann Mendel.


Gregor Mendel1822-1884• Studied science and mathematics (statistics)• Studied heredity (characteristics from parents to

offspring) • Studied garden peas, characteristics, flower

color, height, pod appearance, texture or traits• A trait is a specific characteristic of an individual,

such as seed color or plant height, and may vary from one individual to another.

Led to basic principles of genetics

• Web demo holt• http://my.hrw.com/index.jsp

http://my.hrw.com/index.jsp


Mendel’s Methods• Controlled how plants were pollinated

• Or how the pollen grains produced in the male reproductive parts of a flower (anthers/stamen) to the female reproductive parts of the flower (stigma/pistle)

Two types:

1. Self- pollination

2. Cross pollination


Mendel’s Methods cont:

1. Self- pollination- occurs when pollen is transferred from the anthers of a flower to the stigma of either that flower or another flower on the same plant.

*Can be prevented if remove male parts

2. Cross-pollination- occurs between flowers of two plants, can be specific for traits

*Mendel used this method to study plants

Web demo holt


Mendel’s Experiments

• True-breeding or pure for a trait will produce offspring with a trait of self-pollinate

Ex: yellow pod x yellow pod = yellow pod• Cross pollinated pairs of plants that were true-breeding

for one trait and then another • True-breeding parents were P generation• First generations F1• Second generations F2• Mendel’s crosses

Web demo holt

http://www.dkimages.com/discover/previews/1054/50058372.JPG

Genes and AllelesFrom these results, Mendel drew two conclusions. His first conclusion formed the basis of our current understanding of inheritance.

An individual’s characteristics are determined by factors that are passed from one parental generation to the next.

Scientists call the factors that are passed from parent to offspring genes.

Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting varieties.

These gene variations produced different expressions, or forms, of each trait.

The different forms of a gene are called alleles


Dominant and Recessive TraitsMendel’s second conclusion is called the principle of dominance. This principle states that some alleles are dominant and others are recessive.

An organism with at least one dominant allele for a particular form of a trait will exhibit that form of the trait.

An organism with a recessive allele for a particular form of a trait will exhibit that form only when the dominant allele for the trait is not present.


Segregation

How are different forms of a gene distributed to offspring?

During gamete formation, the alleles for each gene segregate from each other, so that each gamete carries only one allele for each gene.



Results and conclusions• Pair of factors (genes) controlled for traits• Only one trait was visible in F1 generation

(dominant factor)• Traits appeared in the F2 generations in

3:1 ratio (recessive factor)• Law of segregation- pair of factors are

separated during formation of gametes or meiosis

• Law of Independent Assortment- factors separate independently of one another during the formation of gametes (meiosis)

Lesson OverviewLesson Overview11.2 Applying Mendel’s 11.2 Applying Mendel’s

PrinciplesPrinciples


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Key questions?• Differentiate between the genotype and the phenotype

of an organism• Explain how probability is used to predict the results of

genetic crosses• Use a Punnett square to predict the results of a

monohybrid and dihybrid genetic crosses• Explain how a testcross is used to show the genotype of

an individual whose phenotype expresses the dominant trait

• Differentiate a monohybrid cross from a dihybrid cross

Chapter 11 and 14 Genetics 2010


Genetic Crosses

• Today, geneticists rely on Mendel’s work to predict the likely outcome of genetic crosses. In this section you will learn how to predict the probable genetic makeup and appearance of offspring resulting from specified crosses.

Probability and Punnett Squares

How can we use probability to predict traits?

Punnett squares use mathematical probability to help predict the genotype and phenotype combinations in genetic crosses.

Mendel realized that the principles of probability could be used to explain the results of his genetic crosses.

Probability is the likelihood that a particular event will occur.


Probability and Punnett SquaresFor example, there are two possible outcomes of a coin flip: The coin may land either heads up or tails up.

The chance, or probability, of either outcome is equal. Therefore, the probability that a single coin flip will land heads up is 1 chance in 2. This amounts to 1/2, or 50 percent

If you flip a coin three times in a row, what is the probability that it will land heads up every time?

Each coin flip is an independent event, with a one chance in two probability of landing heads up.

Therefore, the probability of flipping three heads in a row is:

1/2 × 1/2 × 1/2 = 1/8

Past outcomes do not affect future ones. Just because you’ve flipped 3 heads in a row does not mean that you’re more likely to have a coin land tails up on the next flip

. 24Chapter 11 and 14 Genetics 2010


Probability• The likelihood that a specific event will

occur.

• Can be expressed as a:– Decimal– Percentage– Fraction

Probability=(# of time event expected to happen)/ (# of time it could happen)

Using Segregation to Predict Outcomes

The way in which alleles segregate during gamete formation is every bit as random as a coin flip.

Therefore, the principles of probability can be used to predict the outcomes of genetic crosses.



Terms1. Genotype- genetic makeup, alleles that

are inherited from parents (PP, Pp, pp)

2. Phenotype- physical appearance (color, height), does not always resemble genotype due to environment factors

3. Homozygous- alleles are the same, can be dominant (PP) or recessive (pp)

4. Heterozygous- alleles are different (Pp)


More terms1. Monohybrid cross- cross with only one

characteristic, offspring are monohybrids2. Punnett square- used to do monohybrid

crosses, used to predict outcomes 3. Genotypic ratio- ratio of genotypes that

appear (1BB: 2Bb: 1bb)4. Phenotypic ratio- ratio of phenotypes

that appear (3 brown : 1 black)5. Test cross- unknown organism is

crosses with a homozygous recessive

How To Make a Punnett Square for a One-Factor Cross

Write the genotypes of the two organisms that will serve as parents in a cross.

In this example we will cross a male and female osprey that are heterozygous for large beaks. They each have genotypes of Bb.

Bb and Bb


How To Make a Punnett Square

Draw a table with enough spaces for each pair of gametes from each parent.

Enter the genotypes of the gametes produced by both parents on the top and left sides of the table.



Fill in the table by combining the gametes’ genotypes.


Determine the genotypes and phenotypes of each offspring.

Calculate the percentage of each. In this example, three fourths of the chicks will have large beaks, but only one in two will be heterozygous.




Types of crosses:A. Homozygous x Homozygous (PP x pp)

B. Homozygous x Heterozygous (PP x Pp) (complete dominance)

C. Heterozygous x Heterozygous (Pp x Pp)

D. Test cross (pp x P_)


Types of crosses:

E. Incomplete dominance- F1 offspring has a phenotype in between that of parents, Cross a white (rr) flower with a Red flower (RR)= pink flower (Rr)


Types of crosses

F. Codominance-both alleles fro a gene are expressed on a heterozygous offspring, neither trait is dominant or recessive, blood types

http://www.biologycorner.com/resources/roancow.jpg

Independent AssortmentHow do alleles segregate when more than one gene is involved?

The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.

Mendel wondered if the segregation of one pair of alleles affects another pair.

Mendel performed an experiment that followed two different genes as they passed from one generation to the next.

Because it involves two different genes, Mendel’s experiment is known as a two-factor, or dihybrid, cross. Single-gene crosses are monohybrid crosses.



Dihybrid crosses

• Two characteristics are tracked, results are dihybrid

Types of crosses( 4 x4 box)

1. Homozygous RRYY x Homozygous rryy

2. Heterozygous RrYy x Heterozygous RrYy (9:3:3:1)

A Summary of Mendel’s Principles

What did Mendel contribute to our understanding of genetics?

Mendel’s principles of heredity, observed through patterns of inheritance, form the basis of modern genetics

At the beginning of the 1900s, American geneticist Thomas Hunt Morgan decided to use the common fruit fly as a model organism in his genetics experiments.

The fruit fly was an ideal organism for genetics because it could produce plenty of offspring, and it did so quickly in the laboratory.

Before long, Morgan and other biologists had tested every one of Mendel’s principles and learned that they applied not just to pea plants but to other organisms as well.

The basic principles of Mendelian genetics can be used to study the inheritance of human traits and to calculate the probability of certain traits appearing in the next generation.



Human Heredity

Chapter 14

p. 390-410


A little Q and ACan you ID some parts to the

chromosomes

- centromere, chromatidsHow many chromosomes are found in the

normal human genome

46 (2n)Each chromosome contains many genes


A little Q and ADifferences between dominant and

recessive

dominance: when an allele that masks the presence of another allele for the same characteristic

Recessive: when an allele that is masked by the presence of another allele for that same characteristic

Can you give examples?


Objectives

• Distinguish between sex chromosomes and autosomes

• Explain the role of sex chromosomes in sex determination

• Describe how an X or Y linked gene affects the inheritance of genes in linkage groups

• Distinguish between chromosomes mutations and gene mutations


Chromosomes and Inheritance

• Francis Collins and his lab group discovered the gene responsible for Cystic Fibrosis. CS is often fatal genetic disorder. Thick, sticky mucus builds up and blocks ducts in the pancreas and intestines and causes difficulty in breathing.

• In this chapter we will learn how diseases and characteristics are inherited and expressed.


Chromosomes

• 1900s Thomas Hunt Morgan experimented with Drosophila melanogaster

• Observed that they had 4pairs of chromosomes

• 3 pairs were identical in male and female

• The fourth pairs was the sex chromosomes XX female, XY male


Sex chromosomes and autosomes

• Sex chromosomes- contain genes that determine the sex (gender) of an individual

• Autosomes- non sex chromosomesSex determination- Sex chromosomes pair during meiosisChild will always receive a x chromosome from the

motherSRY gene- sex-determining Region Y, if have this

gene hormones are released and testes form and if not ovaries form


Can you determine the probability of the sex of the child?

1. Cross a Male and a FemaleXY x XX

2. Set up your punnett square

3. What are your ratios?

4. Who determines the sex of the child?

Sex Chromosomes This Punnett square illustrates why males and females are born in a roughly 50 : 50 ratio.

All human egg cells carry a single X chromosome (23,X).

However, half of all sperm cells carry an X chromosome (23,X) and half carry a Y chromosome (23,Y).

This ensures that just about half the zygotes will be males and half will be females.


Sex Chromosomes

More than 1200 genes are found on the X chromosome, some of which are shown.

The human Y chromosome is much smaller than the X chromosome and contains only about 140 genes, most of which are associated with male sex determination and sperm development.



Effects of Gene location

• Sex-linked genes and traitssome genes are located on the sex chromosomes

Ex: in DM the gene for eye color is located on the X chromosome, Y chromosome lacks this gene

Do this cross:1. (p1) cross an X(R ) X(R ) female red eye with an X(r ) Y male white eye, what is the F1 generation?

Now take two from the F1 and cross them and see what you get?


Sex- linked genes and traits

• The results of these experiments showed Morgan not only genes reside on chromosomes but that red eye color is located on the X chromosome

• Genes can be both x linked or y linked

• Sex linked trait –is coded for by an allele on a sex chromosome


Linked Genes

• Pairs of genes that tend to be inherited together

• Genes are linked because they are found on the same chromosome

• Crossing over during meiosis does not create new genes or delete old ones, just rearranges alleles

• Linkage group- set of linked genes


Chromosome mapping• The farther apart the genes are located on

a chromosome, increases the chance of cross-over

• Chromosome map- diagram that shows the linear order of genes on a chromosome

• Map unit- frequency of crossing-over• Today modern technology has made it

easier to map genes (human genome project)


Mutations• Change in the nucleotide-base sequence of a

gene or DNA molecule• Germ-cell: occurs in an organism’s gametes,

can be passed on to an offspring• Somatic-cell: body cell and can affect the

organism, skin cancer, leukemia, can not be inherited!!

• Lethal mutations- cause death before birth• Can mutations be beneficial to the individual?


Chromosome MutationsTwo ways

1. change in structure of chromosome2. adding or loosing a chromosome

• Deletion- loss of a piecd of a chromosome due to breakage

• Inversion- segments breaks off, flips around and reattaches

• Translocation- breaks off and reattaches to non homologous chromosome

• Nondisjunction- chromosome fails to separate from its homologous during meiosis, get and extra copy (trisomy 21)


Gene Mutations

• Point mutations- substitution, addition, or removal of single nucleotide

• Substitution- one nucleotide replaces another

• Frameshift mutation- it just shifts down- creates new amino acids

• Insertion mutations- addition of a gene and framshift occurs

• ATCGA


Inheritance patterns and human genetics

Human Genetics12.2

241-249


objectives• Analyze pedigrees to determine how genetic

traits and genetic disorders are inherited• Summarize the different patterns of inheritance

seen in genetic traits and genetic disorders• Explain the inheritance of ABO blood groups• Compare sex-linked traits with sex-influenced

traits• Explain how geneticists can detect and treat

genetic disorders


Human Genetics

• This section investigates how genetics analyze genetic data from families to track the inheritance of human genes. It also explores the genetic and environmental factors that influence human genetic traits and disorders, and discusses how geneticists detect and treat human genetic disorders.


Inheritance of traits

Why do geneticists study human genetic traits?

To trace genetic diseases from generation to generation

Study the phenotypes of family members in a pedigree

Pedigrees- diagram that shows how a trait is inherited over several generations


This will be on OGT

Honors:Chapter 9 Patterns of Inheritance

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Patterns of inheritance-Expression of genes over generations• Autosomal traits- appear in both sexes equally• Sex-linked- tend to see only in males, most are

recessive• Carriers- they have one copy of the allele but do

not have the disease, they do not express the disease but can pass it to offspring

-Most are born from normal parents (phenotypically normal) who carries the recessive gene (allele)

-Inbreeding- increases the chances of expression of recessive traits


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inherited disorders

Dominant Disorders- only need one trait

1. achondroplasis- dwarfism

2. Huntington’s – mental deterioration, middle ages

Less likely to be passes if deadly – don’t reproduce


Genetic traits and disorders

• Genetic disorders are diseases that have genetic origin

• Polygenic inheritance- characteristics are influenced by many genes– Skin color (3-6 genes), eye color, height

Complex characters-influenced strongly both by the environment and by genes Skin color is both polygenic and complex,

cancers


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single gene may affect many phenotypic characteristics

• Pleiotropy- genes influence multiple characteristics

example• Fig 9.14 sickle-cell, 1 thing chain events• coloration pattern and crossed eyes of Siamese

cats, which are both caused by the same allele. These unrelated characters are caused by the same protein produced by the same allele.

• gene that causes pigment color in rats. White rats also have very sensitive eyes and often become blind.

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Blood Types - Multiple Alleles and Codominance

• In humans, there are four blood types (phenotypes): A, B, AB, and O

• Blood type is controlled by three alleles. A, B, O • O is recessive, two O alleles must be present for

the person to have type O blood • A and B are codominant. If a person receives an

A allele and a B allele, their blood type is type AB

• Crosses involving blood type often use an I to denote the alleles - see chart.


Multiple alleles

• Having more than 3 alleles

• Blood type ABO, codominance (fig 12.12)– A – B– AB– O


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Codominant and Multiple Alleles This table shows the relationship between genotype and phenotype for the

ABO blood group.

It also shows which blood types can safely be transfused into people with other blood types.

Alleles IA and IB are codominant. They produce molecules known as antigens on the surface of red blood cells.

Individuals with alleles IA and IB produce both A and B antigens, making them blood type AB.



More genetic traitsIncomplete dominance- trait hair, and curly

hair parents have a wavy hair childX- linked- carried on the x chromosomes,

color blindness is a recessive x linkedSex-influenced traits- dependent on male

or female, baldness, have same genotype, tend to be autosomal, hormones play role

Single-allele traits- 200 dominate alleles, Huntington's (HD)autosomal, pass genes before they are aware have it (30-40ys)


Detecting Genetic Disease

• If you have family history see testing

• Genetic screening- Karyotype, blood tests,

• Detect 200 disorders in the fetus by amniocentesis

• Chorionic villi sampling- take cells from zygote between the mothers uterus and placenta between 8-10wks


Karyotype

Questions about a Karyotype?

1. What term do we use to describe the pair of chromosomes?

2. How are the chromosomes that make up each number pair similar?

3. What chromosomes are autosomes?

4. Which are sex chromosomes?

5. Can you explain any abnormalities?


Honors Biology notes-Chapter 8 2008

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Abnormal number of sex chromosomes

• XXY Klinefelter - male sex organs, testes small, individual is sterile, breast enlargement, other female characteristics, normal intelligence (meiosis in egg/sperm)

• XYY normal male- can be taller, (meiosis in sperm)

• XXXnormal female –(meiosis egg/ sperm)• XO Turner syndrome (female, egg/sperm),

sterile, short stature, artificial estrogen

Honors Biology notes-Chapter 8 2008

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Genetic Counseling

• Process of informing a person about the parents or potential new Childs genetic makeup

• Problems that could affect the offspring

• Predict the probability that offspring will be healthy or have a genetic disorder

• Risk factors


Treating genetic diseases

• PKU- lacks the enzyme, causes mental retardation, strict foods, no diet soda, blood tests

• CF- pounding on the back 45min sessionsGene therapy- replacing the defective geneSomatic cell gene therapyGerm cell gene therapy- eggs and spermIs this ethical- how does this affect the next

generation???


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Environment play a role

• Combination of heredity and environmentList some examples

1. mother nature, wind, sun,2. nutrition, exercise, sun3. nature vs nurture

genetic testing- can detect disease-causing alleles

What We Have Learned

In June 2000 scientists announced that a working copy of the human genome was complete.

The first details appeared in the February 2001 issues of the journals Nature and Science.

The full reference sequence was completed in April 2003, marking the end of the Human Genome Project—two years ahead of the original schedule.



The Human Genome Project found that the human genome in its haploid form contains 3 billion nucleotide bases.

Only about 2 percent of our genome encodes instructions for the synthesis of proteins, and many chromosomes contain large areas with very few genes.



As much as half of our genome is made up of DNA sequences from viruses and other genetic elements within human chromosomes.

This chart compares the human genome with other organisms.



More than 40% of our proteins are similar to proteins in organisms such as fruit flies, worms, and yeast.

This chart compares the human genome with other organisms.


What We Have Learned The Human Genome Project pinpointed genes and associated particular sequences in those genes with numerous diseases and disorders.

It also identified about three million locations where single-base DNA differences occur in humans, which may help us find DNA sequences associated with diabetes, cancer, and other health problems.

The Human Genome Project also transferred important new technologies to the private sector, including agriculture and medicine.

The project catalyzed the U.S. biotechnology industry and fostered the development of new medical applications.


New Questions The Human Genome Project worked to identify and address ethical, legal, and social issues surrounding the availability of human genome data and its powerful new technologies.

For example, who owns and controls genetic information? Is genetic privacy different from medical privacy? Who should have access to personal genetic information, and how will it be used?

In May 2008, President George W. Bush signed into law the Genetic Information Nondiscrimination Act, which prohibits U.S. insurance companies and employers from discriminating on the basis of information derived from genetic tests. Other protective laws may soon follow.


What’s Next? The 1000 Genomes Project, launched in 2008, will study the genomes of 1000 people in an effort to produce a detailed catalogue of human variation.

Data from the project will be used in future studies of development and disease, and may lead to successful research on new drugs and therapies to save human lives and preserve health.

In addition, many more sequencing projects are under way and an ever-growing database of information from microbial, animal, and plant genomes is expected.

Perhaps the most important challenge that lies ahead is to understand how all the “parts” of cells—genes, proteins, and many other molecules—work together to create complex living organisms.


intro to genetics

Documents

mendels experiments

mendels results

mendels legacygenetics

mendels methodscontrolled

mendels workdescribe

flower color

delivery of characteristics

laws of heredity