Question

Incorporating gene function during development, what is the distinction between “necessity” and “sufficiency”?

Answer 1

A gene's function is said to be necessary if the mutant shows the defective functioning of a pathway in which it is involved.

A gene's function is said to be sufficient if the WT gene could complement defective functioning of a pathway in which other genes are mutated.

For example, Assume a pathway A ---> B ---> C ---> D

There is another pathway to produce D. X ---> C ---> D

To produce D, all the genes must be functional. If there is a mutation in gene B, the level of D production will be less. So, the function of gene D is necessary to maintain proper levels of D.

However, we could achieve normal levels of D if we overexpress gene C. This shows that gene C is sufficient to maintain normal levels of D.