Master regulatory genes that turn on entire programs of development are often identified because loss-of-function mutations and gain-of-function mutations in the gene have opposite phenotypes. Which type of mutation is recessive? Which type of mutation is dominant?
A)Loss-of-function mutations and gain-of-function mutations are recessive.
B)Loss-of-function mutations are recessive; gain-of-function mutations are dominant.
C)Loss-of-function mutations are dominant; gain-of-function mutations are recessive.
D)Loss-of-function mutations and gain-of-function mutations are dominant.
E)There is no predictable pattern of recessiveness or dominance.

Question

Quizplus · Accepted Answer

Loss-of-function mutations are recessive because one copy of the gene is sufficient to produce enough regulatory protein to activate the developmental program. Gain-of-function mutations are dominant because even one copy of the mutant gene produces enough regulatory protein to activate the developmental program beyond what is normal or necessary. Therefore, loss-of-function mutations are typically homozygous recessive, whereas gain-of-function mutations are typically heterozygous dominant.

Master Regulatory Genes That Turn on Entire Programs of Development