Chapter 17, Problem 28P

Honeybees (Apis mellifera) provide a striking example of environmental effects on eukaryotic gene expression and thus phenotype. Fertile queens and sterile workers are both female bees with the same diploid genomes. However, their morphologies and behaviors are different.

It turns out that the diet of the larval (larvae are young developing insects) females controls their development as either workers or queens. When the hive needs new queens, a few female larvae are fed royal jelly, a substance secreted by worker bees, instead of the normal diet of nectar and pollen. Investigators determined that many genes are more highly CpG-methylated in the larval-stage workers than in the larval-stage queens

a.

Describe an experiment you could do to determine if DNA methylation correlates with differences in gene expression in workers and queens.

b.

Researchers were able to mimic the effect of royal jelly by knocking down the expression in female larvae of a DNA methyltransferase enzyme called DNMT3. (The knockdown was accomplished through a technique called RNA interference that is described in a later problem; the details are unimportant here.) Remarkably, when fed a normal diet, most of these larvae developed as queens. Based on the description of the transgenerational silencing of the $A^Y$ allele of the mouse agouti gene presented in Fig. 17.24, suggest a simple hypothesis that accounts for the different effects on female honeybee larval development of normal versus royal jelly diets.