A position effect variegation (PEV) phenotype can be used to identify new genes that regulate heterochromatin formation. For example, strains of Drosophila melanogaster with the white variegation phenotype can be subjected to mutagenesis to screen for mutations in other genes that suppress PEV, meaning the mutation results in a lower white pigment production. Using what you know about the enzymes that control heterochromatin spreading, describe one mutation that you would expect to be a suppressor of variegation

by mutation of genes encoding histone modification enzymes that lead to loss of gene repression by the alteration of the chromatin structure

Explanation:

Histone methylation is an important epigenetic modification involved in regulation of gene expression. Histone methyltransferases and histone demethylases are enzymes capable of modifying the chromatin structure by adding or removing methyl groups of the N-terminal of the core histones, respectively. There are suppressor of variegation (Su-var) enzymes capable of removing activating chromatin marks such as, for example, histone H3 lysine methylation, thereby mutations in these epigenetic modifiers may result in a loss of gene silencing by directly opening the chromatin structure. For example, Su(var)3–9 is a histone lysine methyltransferase enzyme that controls the formation of heterochromatin.