Degree of Gene Expression

Genes express them by producing visible phenotypes. Some genotypes express themselves faithfully in all the organisms in which these are present. Generally, the structural genes express themselves in all the individuals that carry them. All factors in Mendel’s experiments expressed them completely producing expected phenotypes. Some genes don’t produce the expected phenotype in all cases. The expression of such genes is variable. The measure of gene expression at the population level and at the individual level is denoted under the following two heads:

  • Gene Penetrance
  • Gene Expressivity

Gene Penetrance:

Gene Penetrance is the degree of expression of a gene at the population level. It is the frequency with which a genotype is expressed in the phenotype. It is the proportion of individuals of a given genotype that manifest a phenotype.

Gene Expressivity:

Expressivity of gen is the degree or range of expression of a genotype in those individuals that are supposed to have it. The expressivity differs from penetrance because expressivity denotes the level of expression of phenotype, whereas penetrance is whether the phenotype has appeared or not.