In house flies sex is determined
by M on the Y chromosome.
"Autosomal" or "atypical" strains have been
described where the M factor is located on one or more of the five autosomes
(I-V) or the X. In Florida (FL), 100% of
the males possess the M factor on chromosome III based on collections made in
1973 and 2002 leading to the idea that there is some selective advantage for
autosomal males in FL due to its stability for the past 30 yr. Collections made in 2002 from North Carolina
(NC) had 20% IIIM and 2.35% with both the YM and IIIM
mechanisms in the same individual. Fewer
IIIM males were located in
To study the evolution of sex determination we compared changes in the linkage of M in flies from a NC dairy in 2002, 2006 and in the original population that had been maintained in the lab from 2002-2006. The field collections in both 2002 and 2006 consisted of 78% XYM, 20% IIIM, and <3% with both IIIM and XYM. However, after 4 years in the laboratory, frequencies had changed to 15% XMYM and 85% XYM. These results indicate that the linkage of M can change rapidly or be maintained, depending on the environmental conditions.