The isoenzyme hexosaminidase A (HEXA), composed of subunits α and β, breaks down molecules containing terminal N-acetyl hexosamines.Tay-Sachs disease is caused by a recessively inherited mutation in the gene coding for the α subunit, which is the subunit that hydrolyzes the lipid GM2 ganglioside.Accumulation of this lipid in the brain leads to progressive deterioration of the nervous system and death, usually by age 4.A child born homozygous for the loss-of-function α subunit allele nevertheless does not develop Tay-Sachs disease.Sequence analysis of the β subunit alleles reveals that one allele has a mutation that makes it able to hydrolyze GM2 ganglioside.This is a _______-of-function mutation, which is most likely _______.
A) gain; dominant
B) gain; recessive
C) loss; dominant
D) loss; recessive
E) loss; intermediately dominant

Question

Quizplus · Accepted Answer

The mutation in the β subunit that allows it to hydrolyze GM2 ganglioside compensates for the loss of function in the α subunit, indicating a gain of a new or enhanced function. This mutation would most likely exhibit a dominant pattern of inheritance because only one copy of the mutated β subunit gene is needed to provide the beneficial function of breaking down GM2 ganglioside, preventing Tay-Sachs disease.

The Isoenzyme Hexosaminidase a (HEXA), Composed of Subunits α and β