Question

Which of the following mutations is MOST likely to be recessive?

A.

Deletion of a haplo-insufficient gene

B.

A translocation that fuses a gene to a promoter that causes it to be expressed at the wrong time

C.

An inversion that fuses a gene to a promoter that causes it to be expressed in the wrong place

D.

A high number of CAG repeats within a gene

E.

A high number of CTT repeats in the promoter of a gene, which prevents expression of the gene

Answer 1

Answer A. Deletion of a haplo-insufficient gene is MOST likely to be recessive because a  haploinsufficient gene is described as needing both alleles to be functional in order to express the wild type. One can not describe a mutation as haploinsufficient; instead, one may describe a gene as being haploinsufficient if a mutation in that gene causes a loss of function and if the loss-of-function phenotype is inherited in a recessive manner relative to the wild-type allele.