C-13 Part IINon-Mendelian inheritance

Most phenotypes reflect the influences of several to many genes

and by the environment

Continuous variation• When multiple genes act

together to produce a physical (phenotypic) character, a gradation or range of differences occur.

• Examples: height, weight in humans

• Referred to as polygenic traits

Pleiotropic effects

• Occurs when an allele has >1 effect on phenotype

• Examples are:– Sickle cell anemia

– Cystic fibrosis

Incomplete dominance

• Situation where 2 alleles “blend” to form hybridized phenotype

• Examples:– Flower color in 4

o’clocks and snapdragons

Environmental effects

• Allele expression may be affected by environmental conditions

• Examples:– Coat color in arctic foxes

– Coat color in Himalayan rabbits and Siamese cats

• ch allele affected by temp >33 C tyrosinase enzyme inactivates + reduces melanin pigment production

Epistasis – genes acting “in concert”

• Situation whereby 1 gene pair affects the expression of a 2nd gene pair

• Examples:– Anthocyanin (purple)

pigment in corn

– Animal coat colors

Epistasis (cont’d)• Horse coloration involves 2

or more gene pairings..• EE or Ee is for black• ee is for red (sorrel)• PLUS other genes can add to

base colors• (Bay is AA, EE – black with

agouti gene; Buckskin is AA, EE, CcrC – bay with cremello gene, Dun is AA, EE, Dd – bay with dun gene; Palomino is ee, CcrC – sorrel with cremello gene)

Mutation of genes causes genetic disorders

• Most gene disorders are RARE – nonadaptive

• Most are recessively inherited:– Tay Sachs disease Sickle cell anemia

• Some disorders are inherited in a dominant fashion:– Huntington’s disease

Multiple alleles and Blood Groups

• ABO Blood groups– IAIA and Iai = type A

– IBIB and IBi = Type B

– IAIB and IBIA = Type AB

– ii = Type O

• Rh blood factor• Rh +

• Rh-