Biology Reference
In-Depth Information
Figure 10.4
Sex determination in the house fly,
Musca domestica
.
tra
+
may be equivalent to
da
+
.
F
+
may be equivalent to
Sxl
+
.
tra
+
and
Ag
+
gene products are produced by the mother and stored
in the egg. In the female zygote these products activate the
F
+
gene. The zygote's
tra
+
gene must
be active to maintain the function of
F
+
. This leads to expression of female-differentiation genes,
but the genes lower in the hierarchy are unidentified at present. The
M
+
gene product is present in
males, which represses the
F
+
gene function, so that female-differentiation genes are repressed and
unknown male-differentiation genes are activated. (Modified after
Bownes 1992
.)
other strains of
M. domestica
, both males and females have the
M
factors in the
homozygous state, and the presence or absence of a female-determining domi-
nant factor (
F
) determines sex. Finally, a dominant maternal-effect mutation,
Arrhenogenous
(
Ag
), has been found in
M. domestica
populations that cause
female progeny to develop into fertile males. A recessive maternal-effect muta-
tion,
transformer
, causes genotypic female progeny carrying no
M
factors to fol-
low the male pathway of sexual development to varying degrees. This suggests
that the normal
tra
+
gene product is necessary for female determination and/or
differentiation and that the gene is expressed during oogenesis and in zygotes
(
Inoue and Hiroyoshi 1986
). Experiments suggest that
M
acts early in embryo-
genesis to suppress a key gene, perhaps
F
, whose activity is required continu-
ously for development of females, as is
Sxl
+
in
Drosophila
(
(Hilfiker-Kleiner et al.
1993
).
Meise et al. (1998)
found that
Sex-lethal
+
is not sex-specifically regulated
in
M. domestica
.
