*Lost in Transcription’s* “genetical book review” is a great idea executed well. Not a review of books as literature, but a review of the science in literature.

From the review of *Middlesex*, by Jeffrey Eugenides:

There is a second case of inbreeding, however, that

doescontribute to Cal’s condition. Milt and his wife, Tessie, are second cousins, and each of them is heterozygous for the deficiency. Now, statistically speaking, the fact that Milt and Tessie are second cousins barely counts as incest. For a rare disorder such as 5-alpha-reductase deficiency, the elevation in risk due to a second-cousin marriage is small. How small? Let’s see.Assume that the frequency of the defective version of the gene is q = 0.001, or one in a thousand. This is in the ballpark of what we might expect for a recessive mutation maintained at mutation-selection balance. The probability that an outbred individual inherits two defective copies is approximately q

^{2}, or one in a million. What if the mother and father are related? If their degree of relatedness isr, then the probability that their child will inherit two copies is:

p = q (r/2 + q (1 – r/2))What is this

rthing? Well, if they are brother and sister,r= 1/2, so the probabilitypwould be about 0.00025. For first cousins,r= 1/8, andp= 0.0000634. For second cousins,r= 1/32, andp= 0.0000166.That is, for second cousins, the probability goes from one in a million to about one in 60,000. Basically, you will have a bigger impact by taking prenatal vitamins.

This is joyful stuff. Check them out.