Penetrance = #showing phenotype/total of that genotype
Expressivity refers to the degree to which an individual express the trait.
The environment affects how phenotypes are expressed. The polygenic or continuously varying traits
and the environment lead to a varying degrees of phenotypes in a population. The relative contribution
of nature and nurture differs from environment to environment.
Inheritability: the proportion of the variation of traits, and how the genes/environment causes variation
among a population. E.g. 65% of variation for conservatism is caused by the genetic information, 35%
caused by environment.
Quantitative genetic variation is the basis for selective breeding, concentrating more and more towards
a desired trait. While many evolutionary traits are seen to be continuous, Mendelian theory for 1 or 2
discrete genes are discrete. Edward M. East’s work on tobacco explained how the two could be
combined to explain natural phenomena. East worked on the length of the tobacco flower, which varies
among tobacco populations. He bred two inbred lines with different corolla (flower) lengths. The first
generation of progeny has the same genetic makeup as each other, and has a distribution curve. The
second generation of progeny has a much larger range of corolla length to choose from, this is due to
the recessive genes becoming capable of being expressed. This shows that both genes and environment
plays a part in the expression of the genotypes into phenotypes.
Phenotypic distributions of different genotypes have means among them that