Incomplete and Co-Dominance

Incomplete Dominance One allele is not completely dominant over the other. The heterozygous phenotype is in-between the homozygous phenotypes.

Incomplete Dominance If you cross a RED flower with a WHITE flower, you will get a PINK flower. NOTICE: the RED genotype is RR the WHITE genotype is WW the PINK genotype is RW

Let’s Practice! BW BW BW BW Cross a BLACK chicken (BB) with a WHITE chicken (WW). These alleles show INCOMPLETE DOMINANCE. B B What percent is black? White? Gray? BW BW W Black: 0% White: 0% Gray: 100% BW BW W

Let’s Practice! BW BW BW BW Cross a BLACK chicken (BB) with a WHITE chicken (WW). These alleles show INCOMPLETE DOMINANCE. B B What is the genotype and phenotype of the F1 generation? BW BW Genotype: BW Phenotype: Gray W BW BW W

Let’s Practice! BB BW BW WW What would the cross look like if you crossed two GREY chickens (BW). These alleles show INCOMPLETE DOMINANCE. B W Genotype: 1 BB 1 WW 2 BW Phenotype: 1 Black 1 White 2 Gray What is the genotype and phenotype of the F2 generation? BB BW B BW WW W

Mrs. Smith and Ms. K’s Memory Trick INcomplete is INbetween

Co-Dominance Both alleles contribute to the phenotype. For Example: In chickens, the allele for black feathers is co-dominant with the allele for white feathers. These chickens will have BOTH black and white feathers.

Let’s Practice! BW BW BW BW Cross a Black chicken (BB) with a White chicken (WW). These alleles show CO-DOMINANCE. B B How many chickens in the F1 generation are completely black? White? Black and white? BW BW W Black: 0% White: 0% Both: 100% BW BW W

Let’s Practice! BW BW BW BW Cross a Black chicken (BB) with a White chicken (WW). These alleles show CO-DOMINANCE. B B What is the genotype and phenotype of the F1 generation? Genotype: BW Phenotype: Black and white or checkered. BW BW W BW BW W

Let’s Practice! BB BW BW WW Cross two Black and White (checkered) chickens (BW). These alleles show CO-DOMINANCE. B W Genotype: 1 BB 1 WW 2 BW Phenotype: 1 Black 1 White 2 Checkered List all possible genotypes and phenotypes of the F2 generation. BB BW B BW WW W

Mrs. Smith and Ms. K’s Memory Trick COdominant alleles COllaborate together

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