Question

The wildtype allele of the SYN gene encodes a protein product that stimulates the synthesis of carotenoid pigment in plant leaves. The wildtype homozygote would have 20 units of SYN enzyme and 200ppm (parts per million) carotenoids in its leaves. A mutant for this gene is found which, in the homozygote, produces 20 units of SYN enzyme and 125 ppm carotenoids. The pure-breeding strains are crossed and the F1 produces 20 units of SYN enzyme and 180 ppm carotenoids. The mutant protein differs from wildtype by a single amino acid. Select all of the terms below which could correctly be applied to this system. [HINT: There are FOUR correct choices.]

A. co-dominance

B. dominant negative mutant allele

C. gain-of-function mutation

D. haplosufficent wildtype allele

E. haploinsuffient wildtype allele

F. leaky mutant allele

G. loss-of-function mutation

H. null mutant allele

I. partial dominance

J. simple dominance

Answer 1

In this case , in offspring the SYN gene have 180ppm hence some functions are loss as compared to wild type. So it is a loss of function mutation and in addition, function may remain but less compared to wild type allele hence it is a leaky mutation and not a null mutation. The condition is heploinsufficient because the wild type gene does not produce enough gene product. It is a partial or incomplete dominance condition because the F1 progeny are intermediate between wild type normal allele and wild type mutant allele.