Beyond Dominant and Recessive Alleles Other forms of inheritance

Incomplete Dominance Cases in which no one allele is dominant over the other Cases in which no one allele is dominant over the other –EX: four o’clocks

Usually results in a “blending” of traits!

Codominance Both alleles contribute to the phenotype Both alleles contribute to the phenotype –Feather color in chickens –Black allele and white allele  “erminette” (speckled)

Codominance Let “B” represent black feathers Let “B” represent black feathers Let “W” represent white feathers Let “W” represent white feathers What is the probability of a Black chicken and a erminette chicken having white offspring? Black? Erminette? What is the probability of a Black chicken and a erminette chicken having white offspring? Black? Erminette?

Multiple Alleles Genes that have more than two alleles Genes that have more than two alleles –Coat color in rabbits (p. 273) –Blood type in humans

Blood Type A woman with AB blood type marries a man with O blood. Their child is born with type AB blood. What should the father do? (set up punnett square) A woman with AB blood type marries a man with O blood. Their child is born with type AB blood. What should the father do? (set up punnett square) I A I A I B I B i

Polygenic traits Traits produced by the interaction of more than one gene (many genes) Traits produced by the interaction of more than one gene (many genes) –Wide range of skin color in humans

Sex-Linked Inheritance When a gene is located on the X or Y sex chromosome When a gene is located on the X or Y sex chromosome –The allele for color blindness is recessive and is located on the X chromosome –Let X c represent the colorblindness allele and X the normal allele for females and Y the male chromosome –Show a punnett square explaining why more males are born with colorblindness than females