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Incomplete Dominance Codominance Multiple Alleles Review • Purple Flowers are dominant to White Flowers • Genotypes: ___________________ • Phenotypes: __________________ Review: Dominant/Recessive • Fill-In: The stronger gene or ___________ gene will always mask the weaker gene or _____________ gene PP = purple pp = white Pp = purple Review Problem: Dominant/Recessive • In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants. GENOTYPES: - PP (1); Pp (2); pp (1) - ratio 1:2:1 PHENOTYPES: - purple (3); white (1) - ratio 3:1 P p P PP Pp p Pp pp Incomplete Dominance • What if you did not have completely dominant or completely recessive genes? What if the traits were equally strong? • This is incomplete dominance • The two traits will combine or blend to produce a third trait. • In humans eye and hair color is decided this way. Incomplete Dominance • A third (new) phenotype appears in the heterozygous condition. • 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. GENOTYPES: - Rr (2); rr (2) - ratio 1:1 r Rr rr PHENOTYPES: - pink (2); white (2) - ratio 1:1 r Rr rr R r Codominance • The heterozygous condition, both alleles are expressed equally • 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 GENOTYPES: - NS (2) SS (2) - ratio 1:1 S NS SS PHENOTYPES: - carrier (2); sick (2) - ratio 1:1 S NS SS Multiple Alleles • Some genes have more than two alleles. • One of the best-known examples is the gene that is referred to as the “ABO Blood Group,” which actually has quite a number of alleles. • The three alleles we will work with are symbolized by IA, IB, and i. • However, keep in mind that a person can only have two alleles, two copies of a gene. Thus, the possible genotypes are IAIA, IAi, IBIB, IBi, IAIB, or ii. • (Sometimes, you will see these simplified as AA, AO, BB, BO, AB, and OO, but that does make it harder to remember that these are all alleles for the same gene.) Who is a Donor? • http://www.redcrossblood.org/learn-aboutblood/blood-types 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. O O GENOTYPES: - AO (2) BO (2) - ratio 1:1 A AO AO PHENOTYPES: - type A (2); type B (2) - ratio 1:1 B BO BO 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: -AB (1); BO (1); AO (1); OO (1) - ratio 1:1:1:1 PHENOTYPES: -type AB (1); type B (1) type A (1); type O (1) - ratio 1:1:1:1 A O B AB BO O AO OO In the 1950’s, a young woman sued film star/director Charlie Chaplin for parental support of her illegitimate child. Charlie Chaplin’s blood type was already on record as type AB. The mother of the child had type A and her son had type O blood. • Complete a Punnett square for the possible cross of Charlie and the mother. • The judge ruled in favor of the mother and ordered Charlie Chaplin to pay child support costs of the child. Was the judge correct in his decision based on blood typing evidence? • Explain why or why not.