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Incomplete Dominance Codominance Multiple Alleles

Explore genetic inheritance patterns through examples of incomplete dominance, codominance, and multiple alleles in traits like flower color and blood type. Understand how alleles interact and express in different scenarios.

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Incomplete Dominance Codominance Multiple Alleles

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  1. Incomplete DominanceCodominanceMultiple Alleles

  2. PP = purple Pp = purple pp = white Review: Dominant/Recessive • One allele is dominant over the other (capable of masking the recessive allele)

  3. PP Pp Pp pp Review Problem: Dominant/Recessive • In pea plants, purple flowers (P) are dominant over white flowers (p) show the cross between two heterozygous plants. P p GENOTYPES: - PP (1); Pp (2); pp (1) - ratio 1:2:1 P p PHENOTYPES: - purple (3); white (1) - ratio 3:1

  4. RR = red rr = white Rr = pink Incomplete Dominance • A third (new) phenotype appears in the heterozygous condition. • Flower Color in 4 O’clocks

  5. R r r r Rr Rr rr rr Problem: Incomplete Dominance • Show the cross between a pink and a white flower. GENOTYPES: - Rr (2); rr (2) - ratio 1:1 PHENOTYPES: - pink (2); white (2) - ratio 1:1

  6. NS = some of each SS = sickle cells NN = normal cells Codominance • The heterozygous condition, both alleles are expressed equally • Sickle Cell Anemia in Humans sick

  7. NS SS SS NS 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 S PHENOTYPES: - carrier (2); sick (2) - ratio 1:1

  8. Multiple Alleles • There are more than two alleles for a trait • Blood type in humans • Blood Types? • Type A, Type B, Type AB, Type O • Blood Alleles? • A, B, O (in book – IA, IB, I)

  9. 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

  10. 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) - ratio 1:1 A B PHENOTYPES: - type A (2); type B (2) - ratio 1:1

  11. BO AB AO OO 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: A O • AB (1); BO (1); AO (1); OO (1) - ratio 1:1:1:1 B O PHENOTYPES: • type AB (1); type B (1) type A (1); type O (1) - ratio 1:1:1:1

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