Incomplete Dominance Codominance Multiple Alleles In a nutshell

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 = 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 pp

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: - RR (1); Rr (2); rr (1) - ratio 1: 2: 1 R 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 • There are more than 1 Dominant allele • The heterozygous condition, both alleles are expressed equally • Example: Sickle Cell Anemia in Humans NN = normal SS = sickle cells NS = some of each

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 PHENOTYPES: N/A S NS SS

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 – 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 AO AO PHENOTYPES: N/A B BO BO

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

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