1. How many kinds of 5-membered rings are in DNA?

How many kinds of 6-membered rings are in DNA?

. Drosophila females homozygous for loss-of-function mutations in the gene aubergine are sterile. RNA-Seq experiments show that in the ovaries of these females, the levels of RNAs for many kinds of transposable elements are more than 10× higher than in wild-type ovaries. The aubergine gene encodes a Piwi-family protein.

a. Why do you think these females are sterile?

b. Piwi proteins interact with piRNAs that are transcribed from piRNA gene clusters. Given that the levels of many kinds of TEs are elevated in mutant ovaries, what kinds of DNA sequences do you think are located in these clusters?

c. Many investigators think of piRNAs as a kind of defensive mechanism that protects organisms from the effects of new transposable elements that might be introduced into genomes, for example from other species. Explain.

d. In what way might piRNA systems be beneficial to transposable elements?