Incomplete Dominance Codominance Multiple Alleles In a nutshell!

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

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 PP Pp PHENOTYPES: Pp pp - purple (3); white (1) - ratio 3:1

Incomplete Dominance A third (new) phenotype appears in the heterozygous condition. This new phenotype is a combination of the dominant and recessive trait. Example: Flower Color RR = red rr = white Rr = pink

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

Incomplete Dominance Ratios Incomplete Dominance Genotypic ratio is written as: Homozygous dominant: Heterozygous: Homozygous recessive Incomplete Dominance Phenotypic ratio is written as: Dominant trait: Incomplete trait (mix): recessive trait

Codominance NS = some of each NN = normal cells SS = sickle cells There are more than 1 Dominant allele The heterozygous condition, both alleles are expressed equally Example: Sickle Cell Anemia in Humans NS = some of each NN = normal cells SS = sickle cells

Codominance There are more than 1 Dominant allele The heterozygous condition, both alleles are expressed equally Example: Camilla flowers RR= Red flowers WW= White flowers RW= Red and White flowers

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

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

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

Problem 1: Multiple Alleles Show the cross between a mother who has type O blood and a father who has type AB blood. O O GENOTYPES: N/A A B AO BO PHENOTYPES: N/A

Problem 2: 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 N/A B O AB OO BO AO PHENOTYPES: N/A

Review Complete Dominance: Only either Dominant or Recessive in trait Incomplete Dominance: Dominant, Mixed or Recessive trait Co-dominance: More than one dominant allele (gene)- each expressed equally Multiple Alleles: More than two dominant and or recessive alleles- many trait combinations