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Random Mating

Home > Population Genetics & Statistics > Population Theory > Hardy-Weinberg Principle > Random Mating
A punnet square demonstrating the results of random mating, along with a formula for genotype frequencies: pMM + 2pqMN + qNN = 1

One reason that Hardy-Weinberg does not always apply to humans is that random mating, a condition of HWE, does not occur. Random mating implies that mating should be arbitrary with regard to the locus being considered. As with most mammals, humans tend to mate with individuals that are similar to themselves, especially with respect to evident or visible traits such as height, I.Q., and ethnicity. This constitutes non-random, positive assortative mating. In contrast, negative assortative mating is breeding between individuals with dissimilar genotypes, and is more rare.07 Positive assortative mating leads to an increase in homozygotes whereas negative assortative mating leads to an increase in heterozygotes. However, assortative mating is never complete. While humans often mate with individuals alike in characteristics such as physical attributes, they mate randomly with respect to other traits such as blood type and short tandem repeat (STR) genotype.

Click here to watch a video on random mating presented by Greggory LaBerge.

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NOTE TO USERS: The President’s DNA Initiative DNA Analyst Training program and assessment were completed and published in 2005, in cooperation with the National Institute of Justice. The science and techniques in the program are sound and proven, however, program content has not been updated to include tools and technologies developed and in use after 2005, including many kits and robots. Assessment questions address only content delivered in this program and may not contain the full range of tools in use in your laboratory.