Question

Drosophila geneticists have isolated many mutations that modify position-effect variegation. Dominant suppressors of variegation [Su(var)s] cause less fre- quent inactivation of genes brought near heterochro- matin by chromosome rearrangements, while dominant enhancers of variegation [E(var)s] cause more frequent inactivation of such genes.

A. What effects would each of these two kinds of mutations have on position-effect variegation of the white gene in Drosophila (that is, would the eyes be more red or more white)?
B. Assuming that these Su(var) and E(var) mutations are loss-of-function (null) alleles in the corresponding genes, what kinds of proteins do you think these genes encode?

Answer 1

A. As it is given that Su(var) dominant suppressors of variegation mutant allele causes lesser white patches and more red patches in eyes as it is an inhibits or inactivates of PEV. If the Drosophila were heterozygous for the dominant enhancers of variegation E(var) mutation, there would be less red patches and more white patches.

b. Su(var) 1 gene encodes for the proteins that assist in the spreading of heterochromatin by inhibits the PEV which will be lost by null mutations while E(var)1 gene encodes for the proteins that restrict the spreading of heterochromatin by loss of function mutation