DNA – March 15, 2011

1. What is one example of a genetic disease? Describe it.

2. Show the cross between a Mom who is heterozygous for polydactyl and a Dad who is homozygous recessive for polydactyl.

3. Using your cross from question 2, what is the probability that the offspring will have more than 5 fingers? What is the probability the offspring will be heterozygous?

Today’s Objective

• SWBAT– Understand the difference between codominance

and incomplete dominance

Incomplete Dominance

• Neither of the alleles is dominant to the other.– The phenotype of the offspring is a mixture of the

two phenotypes of the parents.

• This results in a BRAND new phenotype– Example:• Yellow Cow + Blue Cow = Green Cow

Example: Skin Color

Codominance

• The phenotype of the offspring is a combination of the phenotypes of both parents.

• Both alleles are expressed separately and contribute to the offspring’s appearance

• (Unrealistic) Example: – Striped elephant + a polka dot elephant = striped

& polka-dot elephant

Example - Chickens

A black-feathered (BB) chicken crossed with a white-feathered (WW) chicken results in a black and white feathered chicken (BW).

Show the Cross - Codominance

• If a black chicken (BB) and a white chicken (WW) mate, what is that probability that the baby chicken will be black? White? Mixture?

• What happens if a black and white chicken (BW) mates with another black and white chicken? What is the phenotypic ratio?

Incomplete Dominance?

Codominance?

Codominance?

Incomplete Dominance?

Codominance?

Incomplete Dominance?

Practice Problems

Incomplete dominance: B = Black, W = White

1.A black female dog and a white male dog have a litter of puppies. If they have 4 puppies, what does probability predict about the phenotypes of these puppies?

Practice Problems

• Codominance: R = Red, Y = Yellow

2.A female orange panda mates with a male yellow panda. Show the cross and give the phenotypic and genotypic ratios.