Beyond Mendel

Incomplete Dominance Neither allele is completely dominant Heterozygous is a new phenotype, a hybrid, blending Ex. Red snapdragon (RR) is crossed with a white snapdragon (rr) yields all pink snapdragons (Rr)

Codominance Where 2 alleles each affect the phonotype in separate ways. When presented together, both appear Ex. Blood types (AB), Roan horses (red and white hair)

Multiple Alleles When genes exist in more than 2 allelic forms rather than in complete dominance where it was either dominant (D) or recessive (d) Ex. Blood types A, B, O

Pleiotropy When genes affect more than one phenotypic character Ex. If you have cystic fibrosis, the one gene affects respiratory and digestive parts of your body.

Epistasis Two or more genes are involved in determining a particular phenotype. Phenotypic expression of a gene at one locus alters that of a gene at a second locus. Ex. Labrador retrievers (Labs) Black coat dom to brown Genotype is chocolate Second gene determines if pigment will be deposited in hair (ee) yellow

Polygenic inheritance Effect of two or genes on a single phenotypic character. Ex. Skin coloration – 3 genes (A, B and C) AABBCC or aabbcc Cumulative effect, usually results in bell curve Height, eye color