INBREEDING

  • Inbreeding is mating among close relatives. Such breeding can lead to a reduction in genetic variety an an increase in homozygosity. Homozygous means that two identical forms (alleles) of a gene are present. Heterozygous means that two different forms (alleles) of a gene are present.

  • If inbreeding leads to homozygosity, what effect can this have on the population? Well, let's consider an individual who is heterozygous for a rare, deleterious recessive gene. If this individual were to mate with another individual from the population, both individuals probably would not have the same deleterious rare gene. As a result, half of their offspring would be heterozygous like one parent and the other half would be homozygous for the common gene form like the other parent. None of the offspring would be disadvantaged form the mating. Since many forms of genes exist, the chance of two individuals with the same deleterious gene mating is reduced. However, if a population lacks genetic diversity, the chances of individuals with the same deleterious gene mating can be drastically increased. As a result, an unusually large number of abnormalities may occur and the overall fitness of the population can be reduced.
    This information may be found in the following source.
    Ricklefs, R. (1993). The Economy of Nature (3rd ed.). New York: W.H. Freeman and Co.

  • Not only can inbreeding result in an increase in the number of defective phenotypes expressed, but the rate at which a population can adapt to environmental changes may also be lowered. If a population has a small gene pool, it may not be able to respond to rapid changes in the environment. If the environment continues to change and the population cannot adapt because it exhibits low genetic diversity, the population will suffer and may even become extinct.

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