Beyond Dominant Beyond Dominant and Recessive Allelesand Recessive Alleles

Other forms of inheritance Other forms of inheritance

Incomplete DominanceIncomplete Dominance

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

Usually results in a “blending” of traits!

CodominanceCodominance

Both alleles contribute to the Both alleles contribute to the phenotypephenotype– Feather color in chickensFeather color in chickens– Black allele and white allele Black allele and white allele

“erminette” (speckled)“erminette” (speckled)

CodominanceCodominance

Let “B” represent Let “B” represent black feathersblack feathers

Let “W” represent Let “W” represent white featherswhite feathers

What is the What is the probability of a probability of a Black chicken and Black chicken and a erminette a erminette chicken having chicken having white offspring? white offspring? Black? Erminette?Black? Erminette?

Multiple AllelesMultiple Alleles

Genes that have more than two Genes that have more than two allelesalleles– Coat color in rabbits (p. 273)Coat color in rabbits (p. 273)– Blood type in humansBlood type in humans

Blood TypeBlood Type

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

IIAA

IIBB

ii

Polygenic traitsPolygenic traits

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

Sex-Linked InheritanceSex-Linked Inheritance

When a gene is located on the X or When a gene is located on the X or Y sex chromosomeY sex chromosome– The allele for color blindness is The allele for color blindness is

recessive and is located on the X recessive and is located on the X chromosomechromosome

– Let XLet Xc c represent the colorblindness represent the colorblindness allele and X the normal allele for allele and X the normal allele for females and Y the male chromosomefemales and Y the male chromosome

– Show a punnett square explaining why Show a punnett square explaining why more males are born with more males are born with colorblindness than femalescolorblindness than females