5.5 Incomplete Dominance a condition in which the alleles are neither dominant nor recessive results in a blending of traits

Incomplete Dominance examples red flowers crossed with white flowers produce pink flowers brachydactyly

Codominance both alleles are expressed with no blending

Codominance examples roan horses both white & red hairs Andalusian chickens both black & white feathers

Multiple Alleles one of several alleles can be at a given locus example: human blood types

Dominant Alleles Recessive Allele IA and IB Recessive Allele i

Human Blood Types IA IA type A blood IA i type A IB IB type B IB i type B IA IB type AB i i type O

Dihybrid Cross deals with two sets of traits at the same time example: dealing with plant height (tall/short) AND pea color (yellow/green) in the same cross

Independent Assortment The separation of one set of alleles during gamete formation is not affected by the separation of another set of alleles. background: PressArt - Biology text book p.101

Polygenic Inheritance two or more genes affecting the same trait example: human skin color

Sex-Linked Traits 5.6 autosomes sex chromosomes non-sex-determining chromosomes humans = 22 pairs sex chromosomes XX = female XY = male

Female = XX Male = XY X X X X X X X Y Y X Y X

Sex-Linked Traits Some genes are carried on the sex chromosomes. X and Y chromosomes are not homologous. If there is a defective gene on X, the Y would not have a normal gene to counteract it.

Sex-Linked Traits indicated with a superscript above the X and Y chromosomes examples: XH Xh XH Y

Sex-Linked Traits hemophilia human blood disorder lack of a blood chemical that allows for blood clotting

Hemophilia XH Xh carrier female a heterozygous female that does not have the disease but does carry the gene for the trait

Hemophilia XH Xh carrier female XH XH normal female XH Y normal male Xh Xh hemophiliac female Xh Y hemophiliac male