Casual observations on the effects of inbreeding (that is, the mating of close relatives) were probably first made a very long time ago by early breeders of domestic animals. However, Mendel (1865) was the first to describe these effects in a quantitative manner. Consider selfing. A homozygote on selfing gives homozygous offspring only, whereas only half of the offspring of a selfed heterozygote (on average) will be heterozygous. Suppose we take a set of individuals, some of which are homozygous and some heterozygous at a given locus, and self every individual. We expect a reduction in the proportion of heterozygotes as we pass from one generation to the next. If we continue to self successive generations, we expect the proportion of heterozygotes to fall steadily and eventually to reach zero. Mendel gave a formula from which the “expected” proportion of heterozygotes (in a sense we shall define precisely shortly) in any such generation could be predicted. Now this reduction in the proportion of heterozygotes should obtain at every locus; we expect that eventually all individuals will be homozygous at every locus (apart from the occasional heterozygote resulting from new mutation).
KeywordsChromosome Pair Inbreeding Depression Pollen Mother Cell Recombination Fraction Average Total Number
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