Monohybrid cross

A breeding experiment between P generation (parental generation) organisms that differ in one trait.

Monohybrid cross

Mendel's Discoveries:

A. must be a heritable factor that existed in two forms one dominate and one recessive.

He called these factors genes. The dominate and recessive forms of the genes are called alleles.Two factors (alleles) control every trait located on the chromosomes

• B. principle of dominance- only one form of a trait is seen at a time

• C. Law of segregation- 2 alleles for each trait must separate when gametes (sex cells) are formed

• “Your New Baby” activity

Dihybrid cross

• breeding experiment between P generation (parental generation) organisms that differ in two traits.

Lead to the discovery of

Law of independent assortment- genes for traits are inherited separately from one another

Worksheet on Dihybrid crosses

Polygenetic inheritance

A. Definition- inheritance pattern of a trait controlled by 2 or more genesB. Example- skin color is influenced by the effects of 3 to 6 genes. Each gene results in a certain amount of brown pigment (melanin), the more melanin produced the darker the skin, the less melanin produced, the lighter the skin. Polygenetic traits show many degrees of variation

Incomplete dominance

-when two or more alleles influence the phenotype

The phenotype of the heterozygote is between the homozygous dominate and recessive phenotypes

Co dominance causes the phenotype to

express both alleles equally

Multiple Alleles

-Traits controlled by more than 2 alleles-

Example: Blood types

Mutations

-when an existing allele is changed to a new genetic state

• Genes are identified by mutations that alter the phenotype in some conspicuous way.

Types of mutations

1. Chromosomal mutations- changes in the structure of the chromosome such as:

• a. deletion in the information on the chromosome or

Chromosome deletion

b. inversion of the information on the chromosome

c. translocation - when a piece of chromosome information breaks of

and reattaches to another chromosome

• d. nondisjunction - failure of the chromosome to separate during meiosis.

• The gamete will receive an extra copy of a chromosome and the other gamete lacks the chromosome completely.

• Example : Down Syndrome

nondisjunction

Gene mutations

- involve large segments of the DNA or a single nucleotide.

• a. substitutions - substitution, addition or removal of a single nucleotide.

Substitution

Pedigrees- a graphic representation of genetic inheritance

Pedigrees help to trace:

1. Autosomal traits Autosomes 22 pairs of matching homologous

chromosomes NOT carrying information about gender

An autosomal gene will appear in both genders equally

• 2. Sex chromosomes – female = XX male = XY

If a gene is sex-linked ifs effects are seen in one sex

Genes for sex linked traits only found on the X chromosome, it is recessive, and is passed from Mother to son

Colorblindness-

Hemophilia

- inability of the blood to clot following a cut mostly seen in males (Royal families of Europe)

Twins

Of the factors that influence multiple births, there is only one that could be identified as genetic or explained by family history:

hyper ovulation- the tendency to release multiple eggs during ovulation

• Fraternal twins "run in families" on the mother's side only, IF she inherits the gene for hyper ovulation.

Example of how this works

• Generation 1: GrandmaGrandma has the gene for hyper ovulation. She & Grandpa have fraternal boy twins, Rob and Bob

• Generation 2: Rob & Bob While Grandma's sons may carry the gene for hyper ovulation, they do not ovulate. They will not have twins (excluding other factors). However, they each have a daughter.

• Generation 3: Molly & PollyMolly and Polly, cousins, inherit the gene for hyper ovulation from their fathers. They each have a set of twins.

How Genetic disorders are found

I. Genetic screening an examination of a person's genetic makeup.

• This can be done by:

• a. developing a karyotype - a picture of an individual's chromosomes grouped in pairs and arranged side by side. Can see any chromosome abnormalities

• b. testing an individual's blood for the presence or absence of a certain protein.

When is this testing done?

Before birth:a. amniocentesis- Doctor removes a small about

of amniotic fluid from amniotic fluid that surrounds the fetus.

Can be done between 14- 16 wks of pregnancy. The fetal cells and proteins from the fluid and be analyzed and a karotype constructed.

• b. chorionic villi sampling- • doctor removes a sample of the tissue that

grows between the mothers' uterus and the placenta.

• This tissue has the same genetic makeup as the fetus.

• Can be done in the 8th to 10 week of pregnancy.

After birth:

blood tests can be done to check the DNA for genetic disorders

• State: Iowa Current required tests:

• Phenylketonuria (PKU) (Enzyme deficiency• Congenital hypothyroidism (decreased thyroid hormone ) • Galactosemia ( body is unable to use the simple sugar

galactose)• Sickle cell disease • Congenital adrenal hyperplasia (defects in the synthesis

of hormones produced by the adrenal gland

Why do these tests?

Diagnosis and treatment of these disorders can reduce the risk of disease, disability, and even death.

II. Genetic counseling

-a form of medical guidance that informs parents about the problems that could affect their offspring.

Reasons why someone may want counseling

• 1. A couple is planning to start a family and one of them or a close relative has an inherited illness

• 2. An individual already has one child with a severe birth defect

• 3. A woman has had two or more miscarriages.

• 4. A woman is pregnant and over age 34

• 5. A child has medical problems that are recognized as a specific genetic syndrome.

http://www.youtube.com/watch?v=dJuo937gz44

Genetic engineering

- the application of molecular genetics for practical purposes.

- Can be used to identify genes for specific traits or to transfer genes for a specific trait from one organism to another organism

remember that within a cell---chromosome---DNA----gene

Ways that genes can be modified1. manipulating the gene- * use enzymes to cut the DNA sequence and add

a segment of donor DNA.*this new DNA is called recombinant DNA

• When a scientist genetically modifies a plant, they insert a foreign gene in the plant's own genes.

• Example: Gene resistant to pesticide. • The result is that the plant receives the

characteristics held within the genetic code. • the genetically modified plant becomes

resistant to pesticides.

Another type of genetic modification:

Reproductive cloning -the process by which an animal is created which had the same nuclear DNA as a previously existing animal.

Dolly the sheep

• the first large mammal to be cloned by Scottish scientists in 1997,

• Cloned animals are not exact twins • They share copies of the nuclear DNA but

another source of DNA is derived from the original egg

Problems with cloning:

• more than 90% of cloning attempts fail to produce viable offspring.

• little is known of the long-term effects of cloning with many cloned animals dying prematurely.

http://videos.howstuffworks.com/hsw/11818-genetics-cloning-video.htm

Genetic Fingerprinting

• What is it?• a pattern of bands made up of specific

fragments from an individual's DNA

• These patterns can be compared between two individuals to see if they are related.

• DNA fingerprint of different species can also be compared to see how closely related they are.

• used in crime scene analysis to compare samples of blood or hair with a suspects blood or hair

How are they made?

Gel electrophoresis - 1. DNA is extracted from a sample of

blood/tissue. 2. DNA is cut in to fragments using enzymes3. Fragments placed in wells in a gel and an

electrical current is run through the gel for a period of time.4. The DNA fragments which are negative charged migrate to the positive side of the gel.

5. Pores in the gel allow smaller DNA fragments to migrate faster and farther across the gel, than longer fragments, separating the fragments by size.

6. To make the bands visible, the DNA fragments on the gel are split into single chains and blotted onto filter paper. Radioactive elements are added to the filter paper and bind with the DNA fragments.

7. These bands are then exposed to photographic film and the exposed film developed.

8. The bands that developed can then be analyzed.

. Human Genome Project

What is it - 2 goals1. Determine the entire nucleotide sequence of the entire human genome (100,000 genes)

2. Map the location of every gene on each chromosome.

Why do we want this information?

1. Increase our understanding of how genes control the functions of the human body.

2. This knowledge will provide new strategies to diagnose, treat, and possibly prevent human diseases.

3. It will help explain the mysteries of embryonic development and give us important insights into our evolutionary past.

4. Ultimately may make it possible to treat genetic diseases by correcting errors in the gene itself, replacing an abnormal protein with a normal one, or by switching the faulty gene off.

Uses of DNA technology

A. Increasing agriculture yields- genes for enzymes that are harmful to insects can be transferred into plants which protests the plants from the insects.

B. Example : Tomato plant and the hornworm

Tomato Hornworm

Are genetically modified food safe?

• 1. Discuss some food that are modified

• 2. Risks and benefits of genetically modified foods

End unit with possible tour of Monsanto

sources

• chsweb.lr.k12.nj.us (Punnett square• Forum.grasscity.com (dihybrid)• facweb.bhc.edu (Codomininance)• efowl.com (rooster)• ijustlovemychickens.info (Sex-linked chick)• learner.org (blood)• nobelprize.org (Inversion)• skepticwiki.org (trans, deletion)• hhmi.org (down syndrome)• smabiology.blogspot.com (Sickle cell)

Sources cont.

• graphaday.blogspot.com (Color chart)• snider.fwcs.k12.in.us (Color Blind)• en.wikipedia.org (pedigree)• ualberta.ca (hemophilia)• mhhe.com (amnio)• sciencecases.org (cloning)• biology.iupui.edu (gel electro)• omafra.gov.on.ca(hornworm)