The diversity of alleles and genotypes within a population is called genetic variance. The greater the hereditability of a population’s phenotypic variation, the more susceptible it is to the evolutionary forces that act on heritable variation. Heritability is the fraction of phenotype variation that can be attributed to genetic differences, or genetic variance, among individuals in a population. If there is a genetic basis for the ability to run fast, on the other hand, a parent may pass this to a child.īefore Darwinian evolution became the prevailing theory of the field, French naturalist Jean-Baptiste Lamarck theorized that acquired traits could, in fact, be inherited while this hypothesis has largely been unsupported, scientists have recently begun to realize that Lamarck was not completely wrong.
For example, if an athlete works out in the gym every day, building up muscle strength, the athlete’s offspring will not necessarily grow up to be a body builder.
Acquired traits, for the most part, are not heritable. Because alleles are passed from parent to offspring, those that confer beneficial traits or behaviors may be selected, while deleterious alleles may not. Natural selection and some of the other evolutionary forces can only act on heritable traits, namely an organism’s genetic code. Understanding phenotypic variation sources in a population is important for determining how a population will evolve in response to different evolutionary pressures. A number of factors, including the population’s genetic structure and the environment (Figure 1) influence population variation, the distribution of phenotypes among individuals.
We call populations with two or more variations of particular characteristics polymorphic. (credit: Pieter Lanser)Ī population’s individuals often display different phenotypes, or express different alleles of a particular gene, which scientists refer to as polymorphisms. The distribution of phenotypes in this litter of kittens illustrates population variation.
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