MEDizzy - The frequency of carriers of Tay-Sachs disease (MIM*272800)

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Neurosensory and Neuromuscular Systems

The frequency of carriers of Tay-Sachs disease (MIM*272800) in Ashkenazi Jewish populations is 1 in 30. Some Jewish communities offer carrier testing for young adults so they will know their status before marriage. A known carrier female becomes involved with an exchange student from Russia who also is Ashkenazi Jewish but who has not had carrier testing. What is the chance that a child of this union will have Tay-Sachs disease?

ExplanationThe female is a known carrier of Tay-Sachs disease (MIM*272800) and thus has one normal and one Tay-Sachs allele. The male has a 1 in 30 chance of having this same genotype. Each will have a 1 in 2 chance to transmit their abnormal allele to a future child, giving a joint probability of 1/2 × 1/2 × 1/30 = 1/120 (answers a-d incorrect). The joint probability of two or more independent events equals the product of their separate probabilities.