||Modern day whole-genome sequencing and the ability to make comparisons across many
taxa have significantly advanced the study of sex chromosome evolution. The scuttle
fly, Megaselia scalaris, is an appropriate model system for studying sex chromosome
evolution exhibits sex chromosomes that are homomorphic in size, containing differences
that are difficult to detect even microscopically.
Presumably, sex in M. scalaris is determined by the presence or absence of a male-determining
region, or sex realizer (M), that transposes among chromosomes at a low rate, essentially
creating novel Y-chromosomes out of autosomes. M. scalaris would thus serve as a
good model for exploring the primary stages of sex chromosome evolution. However,
to serve as such a model, the identity and size of the male-specific region must be
identified as a boundary within which to search for the sex realizer. This study
focused on elucidating the relative size of the male-specific region in M.
scalaris in relation to the genome. I compared previously generated genome sequences
from male and female M. scalaris to isolate suggested regions unique to the male sex.
Through a systematic approach involving sequencing, primer design, and PCR, I found
the M. scalaris genome to be 27% male-specific, a preliminary result suggesting a
large size inconsistent with published reports. This size further questions observations
pointing to a relatively small male-determining region that transposes, but the male-specific
region may be composed of additional elements unique to the male sex that do not ultimately
determine sex. This study has refined the boundaries within which the sex realizer
(M) of M. scalaris may be located. Future studies are necessary to pinpoint the sex
realizer, an important step towards M.
scalaris’ use as a model system in sex chromosome evolution.