The Genetics of Cousin Marriages
James MacDonald
In much of the world, consanguineous marriage between cousins is very common. For most Americans, however, marriage between cousins is at best a punchline, at worst a taboo. In many states, it is illegal for first cousins to get married. The objections are ostensibly based on the risk of genetic problems. But is there an actual risk?
In 2005, Owen Dyer reported in BMJ that “A Labour MP has called for a public debate on the genetic risks of marriages between first cousins in Britain’s Pakistani community, after reports of an unusually high rate of autosomal recessive disorders among children near her constituency. Ann Cryer, MP for Keighley in West Yorkshire, said on the BBC television program Newsnight: ‘We have to stop this tradition of first cousin marriages.'”
The genetic risks in question are related to something called unmasking. It goes something like this: We each receive one copy of each gene from each of our parents. Thus, we inherit two versions of each gene (called alleles); one is dominant and one recessive. For a recessive gene to actually manifest in an individual, both copies of the gene must be the recessive allele. If an individual inherits only one recessive allele of the gene, the individual is considered a carrier who can pass on the illness to their offspring. But when an individual inherits two copies of a dangerous recessive allele, they the gene is said to be unmasked and inherit the condition.
Additional story and graph at: https://daily.jstor.org/the-genetics-of-cousin-marriage/
https://daily.jstor.org/the-genetics-of-cousin-marriage/
