Heredity refers to the distribution of variation in phenotypes in a population due to genetic variation. Heritability measures the contribution of genetic factors to differences in phenotype, with two statistical measures: broad sense and narrow sense. Both environment and genotype contribute to phenotypic makeup, and heritability rates can be established. The two measures of heritability examine different aspects of genetic variance, with the strict sense being the most widely used. Biologists use this measure to determine how a population may respond to natural selection.
Heredity is a term used in biology and population genetics to refer to the distribution of variation in phenotypes in a population that results from genetic variation. Phenotype is the outward appearance of a particular characteristic in an organism: human height is one example. The emergence of a specific trait can be caused by environmental or genetic factors. Heredity measures the contribution of genetic factors to differences in phenotype. There are two different statistical measures of heritability: broad sense and narrow sense.
In any given population of organisms, there is variation in phenotypes. A certain proportion of these phenotypes are produced by environmental conditions, while another proportion is caused by the organism’s genotype, or its genetic makeup. For example, a person’s height is influenced by both their genes and their environment. Good nutrition can produce taller people, but also tall parents. Both factors are influential in producing the tall phenotype.
Since both environment and genotype contribute to the phenotypic makeup of a population, a heritability rate can be established. If all differences between individuals in a population are caused by genetics, heredity is considered to be 1.0. On the other hand, if environment is the only factor contributing to differences in phenotype and genetics contributes nothing, heredity is 0.0. Subtracting the heritability measure from 1.0 gives the environability measure, which is the proportion of phenotypic variation caused by environmental factors.
The two measures of heritability, broadly and narrowly, examine different aspects of genetic variance. Genetic variance is the amount of variation in the phenotype due to genetic differences among individuals in the population. It differs from heredity, which is a strictly proportional measure. Additive genetic variance refers only to phenotypic variance inherited through the presence of an allele, a specific form of a gene. Other types of genetic variance, such as dominance variance, analyze the variation in a population caused by interactions between alleles.
The strict sense is the most widely used measure because it focuses on a trait of interest. Biologists use this measure to determine how a population may respond to natural selection – the elimination of some individuals and their genotypes due to the higher reproductive success of other individuals. Heredity in the broad sense incorporates all possible sources of genetic variance, including interactions between genes, in its proportional extent.
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