1. Niemann-Pick is an autosomal recessive disease in humans. Mutation of a gene

Question

1. Niemann-Pick is an autosomal recessive disease in humans. Mutation of a gene involved in lipid storage called Sphingomyelin phosphodiesterase1 (SMPD1) is responsible for pleiotrophic phenotypic defects of an enlarged liver and spleen, and neurological disorders including unsteady gait, slurring of speech and the gradual loss of intellectual abilities. The incidence of Type A Niemann-Pick disease worldwide is 1 in 250,000. Assuming random mating (i.e., H-W equilibrium), what is the frequency of heterozygous carriers of Niemann-Pick in the worldwide population?

Explanation / Answer

The number of recessive alleles, q2 = 1/ 250, 000; q = 0.002

Since p+ q = 1, p = 1- 0.002 = 0.998

Frequency of heterozygous carriers = 2pq = 2* 0.998* 0.002 = 0.00399 = 0.004 (approximately) = 100/ 25, 000 or

1000/ 250, 000.

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