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### Transcript of Dominance - Loudoun County Public Incomplete Dominance •Codominance. Incomplete Dominance...

• Dominance

Relationships

• Recap

So

If you show the dominant phenotype, what could your genotype be?

What is genotype and phenotype again?

• If you are unsure if the organism is a pure-

bred, you can do a Test Cross

Test Cross: Cross the individual that shows dominant phenotype with a recessive individual

If offspring 100% dominant

Original was pure (HD)

If offspring not 100% dominant

Original was heterozygous

• Predicting a Test Cross

• Remember, Punnett Squares are usually good only for single-gene traits.

A a

A

a Aa

AA Aa

aa

Looking at just one trait is called a MONOHYBRID Cross

• Looking at TWO traits in one Punnett Square is called a DIHYBRID Cross

• TRY A DIHYBRID CROSS!

Show the probabilities of a cross between two people, both heterozygous Full Lips (Ff), Clefted Chin (Cc)!

F = Full Lips (dominant), f = Thin Lips (recessive)

C = Cleft Chin (dominant), c = Non-clefted Chin

The hardest part is segregating the alleles

• FfCc X FfCc

Ff Cc

Ff C

c

FC

FC FFCC(full lips, cleft chin)

Finish Up!

Fc fC fc

• Numbers:

How many Full Lips/Clefted Chins? _____

How many Thin Lips/Clefted Chins? _____

How many Full Lips/Non-clefted? _____

How many Thin Lips/Non-clefted? _____

___:___:___:___

9:3:3:1 -This is the classic ratio for a heterozygous dihybridcross!

9/16

3/16

3/16

1/16

9 3 3 1

• Dominance Relationships

Complete dominance: one allele shows full dominanceover the other (dominant v. recessive)

Incomplete dominance: neither allele is fully dominant over the other (mixed phenotype)

Codominance: Both alleles dominant; one phenotype wins (shows) in some cells, the other shows in other cells (either can show)

• Which Is This

Complete Dominance

Incomplete Dominance

Codominance

• Which Is This

Complete Dominance

Incomplete Dominance

Codominance

• Which Is This

Complete Dominance

Incomplete Dominance

Codominance

http://creationwiki.org/File:Brown_eyes.jpg

• Which Is This

Complete Dominance

Incomplete Dominance

Codominance

http://creationwiki.org/pool/images/c/c6/Codominant.jpg

• Incomplete Dominance

In northeast Kansas there is a creature know as a wildcat. It comes in three colors, blue, red, and purple. This trait is controlled by a single gene with incomplete dominance.

A homozygous (BB) individual is blue, a homozygous (bb) individual is red, and a heterozygous (Bb) individual is purple.

What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one?

Cross a Purple Cat and a Red cat. Can they have Blue offspring?

http://www.ksu.edu/biology/pob/genetics/defin.htmhttp://www.ksu.edu/biology/pob/genetics/defin.htmhttp://www.ksu.edu/biology/pob/genetics/defin.htmhttp://www.ksu.edu/biology/pob/genetics/defin.htm

• Co-Dominance

Longhorns may be white (CWCW), red (CRCR) or roan (CRCW). Roan longhorns have a mixture of both white hairs and red hairs due to a codominant gene.

Cross a Roan Bull with a Red Female! What are the genotypes and Phenotypes?

Can roan cows produce more roan cows?

http://www.vetmed.ucdavis.edu/cvec/foley_web_site/ef0030_white-cow.jpg