Silkworm, Bombyx mori
Insects have a variety of systems for determining male and female. Some like the Drosophila Fly, Drosophila melanogaster,
have an XY system similar to humans: Females have two copies of an X chromosome (XX), Males have one X and one Y chromosome (XY). A similar sex determination system makes Drosophila
an even more useful model for human genetics. The silkworm sex determination system has been an enigma. Like some reptiles and birds, silkworms have a ZW sex determination system. Males are ZZ and Females are ZW. A factor on the W chromosome, when present, produces females, but identifying that factor has been elusive. The silkworm W chromosome lacks DNA sequences that encode proteins. Instead, the DNA produces RNA that interacts with proteins (pi-RNA).
One such RNA produced by the W chromosome, named “Fem” is the precursor of an RNA that silences the Masc gene. The Masc gene produces a protein causes the insect to express male features. A male silkworm with two Z chromosomes (ZZ) produces the Masc proteins and has male features. A female silkworm has a W chromosome that produces Fem and silences the Masc gene on the Z chromosome. A female produces very little Masc protein and has female features. Comparisons of sex determination in different species leads to a deeper understanding of the sex determination process in all species.
Read More: A single female-specific piRNA is the primary determiner of sex in the silkworm. Takashi Kiuchi, Hikaru Koga, Munetaka Kawamoto, Keisuke Shoji, Hiroki Sakai, Yuji Arai, Genki Ishihara, Shinpei Kawaoka, Sumio Sugano, Toru Shimada, Yutaka Suzuki, Masataka G. Suzuki & Susumu Katsuma. 2014. Nature 509: 633–636
Jonathan Neal is a retired Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010).
This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog.
The opinions and materials posted here are those of the author and are in no way connected with those of my employer.