Codominance Notes Mrs. Callan 2017

Codominance Codominance - If offspring phenotype is heterozygous, the offspring will exhibit BOTH traits from the parents. NO BLENDING! Both dominant and recessive traits expressed. USE CAPITAL LETTERS FOR PUNNETT SQUARES. Examples: Blood types in humans, sickle-cell disease, coat color in dogs, cattle and horses

ROAN Codominance in Cattle Red Cattle = RR (homozygous) White Cattle = WW (homozygous) Roan (Red & White Hair) = RW (Heterozygous) ROAN

Example Problem #1 Cross a roan cow and a white cow. Key: RR = Red WW = White RW = Roan (Red & White) R W W RW WW Genotypes: 2/4 50% RW 2/4 50% WW Ratio 2:2 Phenotypes: 2/4 50% Roan 2/4 50% White W RW WW

Codominance in Chickens Black Chicken = BB White Chickens = WW Andalusian (Black & White) = BW

B W B BB BW B BB BW Key: BB = Black WW = White Example Problem #2 Cross a black & white Andalusian chicken with a black chicken. Key: BB = Black WW = White BW = Black & White (Andalusian) B W B BB BW Genotypes: 2/4 50% BB 2/4 50% BW Ratio 2:2 Phenotypes: 2/4 50% Black 2/4 50% Andalusian (B&W) B BB BW

Codominance in Human Blood Human blood types are determined by genes that follow the codominance pattern of inheritance. There are two dominant alleles A and B and one recessive allele O. Possible blood types are: Type O = OO Type AB = AB Type A = AA (Homozygous) or AO (Heterozygous) Type B = BB (Homozygous) or BO (Heterozygous)

Example Problem #1 Create a Punnett Square showing all the possible blood types of the offspring produced by a “O” mother and a Type “AB” father. O O Key: Type O = OO Type AB = AB Type A = AA (Homozygous) or AO (Heterozygous) Type B = BB (Homozygous) or BO (Heterozygous) AO AO A BO BO B

Example Problem #1 Create a Punnett Square showing all the possible blood types of the offspring produced by a “O” mother and a Type “AB” father. O O Genotypes: 2/4 50% AO 2/4 50% BO Phenotypes 2/4 50% Type A Blood 2/4 50% Type B Blood AO AO A BO BO B

Example Problem #2 Create a Punnett Square showing all the possible blood types of the offspring produced by a heterozygous Type A mother and a Homozygous Type B father. A O Key: Type O = OO Type AB = AB Type A = AA (Homozygous) or AO (Heterozygous) Type B = BB (Homozygous) or BO (Heterozygous) AB BO B AB BO B

Example Problem #2 Create a Punnett Square showing all the possible blood types of the offspring produced by a heterozygous Type A mother and a Homozygous Type B father. A O Genotypes: 2/4 50% AB 2/4 50% BO Phenotypes: 2/4 50% Type AB Blood 2/4 50% Type B Blood AB BO B AB BO B