Bio exam 3 - Exceptions to Mendelian Genetics and Pedigrees

Incomplete dominance

“In between” phenotype; the phenotype of heterozygotes is between both of the homozygote phenotypes; ex red snapdragon x white snapdragon = pink snapdragon

Codominance

2 different alleles can be expressed at the same time; each allele produces a distinct phenotype that can be detected in heterozygous individuals; ex red blood cells - Ai/Bi = type A or B, ii = type O, but AB = type AB and both the A antigen and B antigen are expressed

Epistasis

When one gene changes the phenotype of another gene; phenomenon where one gene affects the expression of a second gene; ex red blood cells - protein made by H gene attaches antigens to blood cell (line), so if the blood cell is hh/homozygous recessive, it will be type O even if it has the A or B genotype bc the antigen cannot be attached

Incomplete penetrance

When, of individuals with a specific genotype, a proportion show the phenotype and a proportion do not show the phenotype; penetrance refers to the all or none expression of a genotype; Ex polydactyly genotype is autosomal dominant (DD or Dd) and 80% penetrant, so 80% of people with the gene actually have extra fingers/toes, while 20% don’t even though they have the genotype

Variable expressivity

When all individuals with a specific genotype express the phenotype, but to varying degrees/extents; ex some people with polydactyly have 1 extra toe and some have 5

Pedigrees

Symbolic representations of family relationships and the transmission of inherited traits; helps families identify the risk of transmitting an inherited illness

Autosomal recessive trait

The trait may skip one or more generations; ex albinism

Autosomal dominant trait

Does not skip generations and can affect both sexes; ex polydactyly