Nonrandom Mating


Nonrandom mating occurs when there is discrimination between potential mates and selection or rejection of them based on their phenotypical characteristics. This deviation from random mating results in predictable changes in genotype frequencies in subsequent generations.

Keywords: nonrandom mating; positive assortative mating; negative assortative mating; inbreeding; consanguineous mating

Figure 1.

Punnett square. A simple graphical method developed by Reginald Punnett in the early twentieth century to calculate all of the potential combinations of offspring genotypes that can occur and their probability given the parent genotypes. The statistical results of Punnett squares are based on the assumption of an infinite number of successful matings and the absence of evolutionary mechanisms.

Figure 2.

Consanguineous mating patterns and the coefficients of inbreeding (F) for the resulting children. Triangles represent males, circles are females, equal signs indicate sexual unions, vertical lines show descent bonds and horizontal lines show codescent bonds.

Figure 3.

Exogamy and endogamy operate simultaneously in limiting mate selection.

Figure 4.

Relationship between unilineages, clans, phratries and moieties.



Bennett RL, Motulsky AG, Bittles A, et al. (2002) Genetic counseling and screening of consanguineous couples and their offspring: recommendations of the National Society of Genetic Counselors. Journal of Genetic Counseling 11(2): 97–119.

Bittles AH (2001) A Survey of the Current Global Prevalence of Consanguineous Marriage. Perth, Australia: Centre for Human Genetics, Edith Cowan University. (Available online (see Web Links).)

Bittles AH, Savithri HS, Venkatesha Murthy HS, et al. (2001) Human inbreeding: a familiar story full of surprises. In: Macbeth HM and Shetty PS (eds.) Health and Ethnicity, pp. 68–78. London, UK: Taylor & Francis.

Bittles AH, Shami SA and Appaji Rao N (1992) Consanguineous marriage in southern Asia: incidence, causes and effects. In: Bittles AH and Roberts DF (eds.) Minority Populations: Genetics, Demography and Health, pp. 102–118. London, UK: Macmillan.

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Further Reading

Bittles AH and Neel JV (1994) The costs of human inbreeding and their implications for variations at the DNA level. Nature Genetics 8: 117–121.

Hartwell LH, Hood L, Goldberg ML, et al. (2000) Genetics from Genes to Genomes. Boston, MA: McGraw‐Hill.

Schull WJ and Neel JV (1965) The Effect of Inbreeding on Japanese Children. New York, NY: Harper and Row.

Sutton HE (1980) An Introduction to Human Genetics, 3rd edn Philadelphia, PA: Saunders College/Holt, Rinehart and Winston.

Web Links, Alan Bittles, Edith Cowan University, Australia. Extensive clearinghouse of academic and government information concerning the cultural patterns and statistics of consanguineous unions around the world current information about changing laws and social trends relating to cousin marriages. This is primarily an advocacy site focused on North America

Nature of Kinship, Dennis O'Neil, Palomar College, USA. Anthropological tutorial about types of descent systems and family organizations found around the world. Kinship terminology and concepts are presented

NCBI Genes and Disease, US National Center for Biotechnology, National Library of Medicine, National Institutes of Health. Descriptions of genetic disorders referenced by chromosome number and general disease category (cancer, immune system, metabolism, muscle and bone, nervous system, signals, and transporters)

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O'Neil, Dennis H(Jul 2006) Nonrandom Mating. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0005448]