Question

Alcohol dehydrogenase is an enzyme composed of several polypeptide subunits. It is normally expressed at high levels in the liver and the lining of the stomach. It is essential to metabolize alcohol, as without it, drinkers would become drunk faster and stay drunk longer. A scientist is studying mutations in mice that affect the activity of the enzyme. She finds that a heterozygote having a normal allele and a mutation that deletes the gene has 50% of normal enzyme activity. She has identified a new mutation and generated a homozygote for it. She crosses this homozygote to the deletion-bearing heterozygote. Half of the offspring have 50% of normal enzyme activity and half of the offspring have 0% of normal enzyme activity. Select all answers that correctly characterize the new mutation.

A.It is a null mutation.

B.It is dominant negative.

C.It is a loss-of-function mutation.

D.It is a gain-of-function mutation.

E.It is a partial loss-of-function mutation.

F.It is haploinsufficient

Answer 1

Let the normal gene be A, let the allele with deletion be a- and new mutant allele be a

Aa- has 50% of the normal enzyme, means a- is not producing any normal enzyme but A in Aa- can produce normal enzyme as it is in AA, since only one allele is functional 50% of the protein is functional

then Aa- * aa

	A	a-
a	Aa	aa-

the ratio of offsprings is Aa: aa-=1:1

observed is Half of the offspring have 50% of normal enzyme activity and half of the offspring have 0% of normal enzyme activity. Aa has 50% normal enzyme and aa- has no functional enzyme, means a- and a alleles cannot produce a functional protein

based on this information

a is a null mutant allele and it is a complete loss of function mutation

so answers are A.It is a null mutation,

C.It is a loss-of-function mutation.