C-13 Part II Non-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 2 nd 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 diseaseSickle cell anemia Some disorders are inherited in a dominant fashion: –Huntington’s disease

Multiple alleles and Blood Groups ABO Blood groups –I A I A and I a i = type A –I B I B and I B i = Type B –I A I B and I B I A = Type AB –ii = Type O Rh blood factor Rh + Rh-