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Genetics Overview: Incomplete Dominance, Codominance, and Multiple Alleles

Understand the concepts of incomplete dominance, codominance, and multiple alleles through genetic examples. Learn how different genotypes result in unique phenotypes in offspring.

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Genetics Overview: Incomplete Dominance, Codominance, and Multiple Alleles

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  1. Incomplete DominanceCodominance A Quick Review

  2. Incomplete Dominance • A third (new) phenotype appears in the heterozygous condition.

  3. Incomplete Dominance Example 1 • In blue blahblah bird & a white blahblah bird produces offspring that are silver show the cross between two heterozygous birds. BW GENOTYPES: - BB (1); BW (2); WW (1) BW B W BB WW BW PHENOTYPES: • Blue (25%); Silver (50%); White (25%)

  4. Incomplete Dominance Example 2 • In blue blahblah bird & a white blahblah bird produces offspring that are silver show the cross between a blue bird and white bird. BB GENOTYPES: - BW (4) BW BW W W PHENOTYPES: BW BW - Silver 100%

  5. Codominance • The heterozygous condition, both alleles are expressed equally. • In some chickens, the gene for feather color is controlled by codominance. The heterozygous phenotype is known as erminette (spotted chickens).

  6. CodominanceExample 1 • A white chicken is crossed with erminette (spotted chickens). W W GENOTYPES: - BW (2) and WW (2) BW BW B W PHENOTYPES: WW WW - spotted chickens 50% and White 50%

  7. Multiple Alleles • There are more than two alleles for a trait • A and B are codominant • AA = Type A • BB = Type B • AB = Type AB • A and B are dominant over O

  8. AO AO BO BO Problem: Multiple Alleles • Show the cross between a mother who has type O blood and a father who has type AB blood. O O GENOTYPES: - AO (2) BO (2) A B PHENOTYPES: - type A (50%); type B (50%)

  9. AO AA AB BO Multiple Alleles Example 1 • Show the cross between a mother who has type AO blood and a father who has type AB blood. A O GENOTYPES: - AO (2) BO (1) AB (1) A B PHENOTYPES: • type A (50%); type B (25%) • Type AB 25%

  10. BO AO AO BO Multiple Alleles Example 2 • Show the cross between a mother who has type AB blood and a father who has type OO blood. A B GENOTYPES: - AO (2) BO (2) O O PHENOTYPES: • type A (50%); type B (50%)

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