Incomplete Dominance Codominance Multiple Alleles

Review: Dominant/Recessive One allele is dominant over the other (capable of masking the recessive allele) –This is called complete dominance. *All the problems done in class thus far have been with complete dominance.* PP = purple pp = white Pp = purple

Review Problem: Dominant/Recessive In pea plants, purple flowers (P) are dominant over white flowers (p) show the monohybrid cross between two heterozygous plants. GENOTYPES: PHENOTYPES:

Incomplete Dominance A third (new) phenotype appears in the heterozygous condition. Instead of dominant and recessive, there is more of a “blending” of alleles Ex: Flower Color in 4 O’clocks RR = red rr = white Rr = pink

Problem: Incomplete Dominance Show the cross between a pink and a white flower. R r rrrr GENOTYPES: PHENOTYPES:

Problem: Incomplete Dominance Hair Texture in humans is a result of incomplete dominance. What would be the outcome of crossing a person who is homozygous for straight hair with a person who is homozygous for curly hair?

Codominance The heterozygous condition, both alleles are expressed equally No recessive condition Ex: Sickle Cell Anemia in Humans NN = normal cells SS = sickle cells NS = some of each

Problem: Codominance Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick. N S SSSS GENOTYPES: PHENOTYPES:

Problem: Codominance The roan pattern in a cow’s coat is a result of codominance. Using the square below, what would be the outcome of crossing a roan bull (Rr) with a white cow (rr)?

Multiple Alleles There are more than two alleles for a single trait Ex: Blood type in humans Blood Types? –Type A, Type B, Type AB, Type O Blood Alleles? –A, B, O (in book – I A, I B, I)

Rules for Blood Type A and B are codominant –AA = Type A –BB = Type B –AB = Type AB A and B are dominant over O –AO = type A –BO = type B –OO = type O

Problem: Multiple Alleles Show the cross between a mother who has type O blood and a father who has type AB blood. GENOTYPES: PHENOTYPES: O O ABAB

Problem: Multiple Alleles Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood. GENOTYPES: PHENOTYPES:

ORIGINAL SLIDES CREDITED TO: PALATINE HIGH SCHOOL