Codominance•When there are at least 2 usually 3 alleles that influence a trait.

–1 is recessive. –The other 2 are dominant to that allele but not to each other.

Human

Blood Types

In the human population, there are 3 major alleles for the surface protein gene: A, B, and O.

A

B

O

A and B are dominant to O but not to each other

Recessive

Genotype Phenotype

AA or AO

IAIA or IAi

Type A

BB or BO

IBIB or IBi

Type B

AB

IAIB

Type AB

OO

ii

Type O

Human Blood Types

CodominanceCodominance

• Example:Example: homozygous male B (IBIB)

x heterozygous female A

(IAi)

IAIB IAIB

IBi IBi

1/2 = IAIB

1/2 = IBi

IA

IB IB

i

CodominanceCodominance

• Example:Example: male O (ii) x female AB (IAIB)

IAi IBi

IAi IBi

1/2 = IAi1/2 = IBi

i

IA IB

i

Codominance

• In codominance, the alleles are neither dominant, nor recessive. Neither allele is masked by the other.

Roan CowIs both white and red

Chestnut or Red Roan

Black or Blue Roan

Palonimo

Mystery Bull Experiment

• http://tepserver.ucsd.edu/people/Tracee-Parsons/Final-genetics-project/mystery-bull.html

Through genetic engineering, you and your partner, Maisie have developed a new type of corn. You have named it WonderCorn.

•It has a tasty flavor of butter and salt. •The good thing about this new corn is that you do not have to add butter and salt to it once it is cooked. •This makes it a much healthier dish.

Flav-R-Gro, Inc.

You and Maisie suspect that the taste trait is corn in codominant. To find out, you crossed two other types of corn: a homozygous salty corn (SS) and a homozygous buttery corn (BB). The offspring were all WonderCorn.

Create the Punnett Square

S S

B

B

SB SB

SB SB

What is the genotype of WonderCorn?

What percent of the offspring will have this genotype?

S B

S

B

You were correct. Taste is a codominant trait.

Make a Punnett Square showing a second-generation cross. (Both parents are heterozygous)

What percent of the offspring will be WonderCorn?

SS SB

SB BB

50 % will be WonderCorn.

1:2:1 Ratio

The demand for WonderCorn is high. Grover’s Grocery has already ordered 50 bushels and wants more. You are all out. You are at the beginning of a new growing season. Would you be better off using homozygous plants to grow or heterozygous? Why?

Do the math!

• If a heterozygous cross produces 736 offspring, how many will be WonderCorn?

• How many of the 736 offspring will taste salty but not buttery?

50% of 736 = 368 25% of 736 = 184

Quiz

Tomorrow