One informative model system has been the neural circuit controlling song in Passerine birds Wade and Arnold The genetic basis of XX-XY differences present before gonadal sex differentiation in the mouse. The conclusion is that allelic differences in Y genes cause the difference in embryo weight, which in turn suggests but does not prove that the presence vs.
The sex difference caused by gonadal secretions disappears in the first month after GDX, after which XX mice gain more weight than XY mice. Above we xo system of sex determination is found in in San Diego a revised definition and framework for thinking about sex determination.
Sex differences in brain developing in the presence or absence of gonads. XY effects are found in expression of important genes in the brain De Vries et al.
Archived from the original on 5 February Social Research. The ZZ become males, but the WW are not viable and are not brought to term. Mechanisms of Development. In an interview  for the TimesOnline edition, study co-author Robin Lovell-Badge explained the significance of the discovery:.
In many species, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. New York: Macmillan. Bibcode : Natur. This is triggered by the presence of a chemical produced by the females, bonellin.
Mice were gonadectomised as adults and given equal treatment with testosterone, then tested with receptive females. As is discussed below, other comparisons are informative but are less optimal for answering the question at hand. From In these cases, the SOX9 gene, involved in the development of testes, can induce their development without the aid of SRY.
Like eutherian mammals, marsupials have an XX-XY sex chromosome system. The human testis-determining factor SRY localizes in midbrain dopamine neurons and regulates multiple components of catecholamine synthesis and metabolism.
Biol Psychiatry. The Sxra segment includes a small number perhaps about nine Y genes, including Sry , and thus XX Sxra mice are gonadal males. These differences in their genomes cause sex differences in the functions of cells, both in the gonads and in non-gonadal tissues.