The most complete models integrate a vast array of data, including a list of all genes expressed in the cell or tissue of interest, the molecular function of those genes, information on cis regulatory elements and trans regulatory factors, and gene expression profiles after numerous gene perturbation experiments [ Bolouri and Davidson, ; Friedman, ].
In contrast, ovaries develop when the outer cortex i. Extended production of the Mullerian duct regressor in the American alligator. Occasionally, there are hermaphrodites in place of one or both sexes. Several approaches could be used to distinguish these genes, including linkage studies, gene perturbation studies i.
Sex Determination Although the specific molecular mechanism that determines sex has not been revealed in any reptilian species, general modes of sex determination can be described [ Bull, ; Janzen and Paukstis, ].
A variety of such regulatory mechanisms have been described so far and some of the more extensively studied ones are being discussed. Immunological reactions and cytokine levels may also be important. General and Comparative Endocrinology. In addition, endocrine signals from the testes i.
All this takes place early in development, leading to the activation of the sxl gene through an "early" promoter in females. Finally, a third stage in X-Y evolution is placed 80 to million years ago and a final one 30 to 50 million years ago, coinciding with primate initial appearance.
Subfertility and defective folliculogenesis in female mice lacking androgen receptor. However, it is important to note that these gene regulatory models are hypothetical and that they require experimental testing before firm conclusions are drawn.
The latter is communicated early in development through the delicate balance between the dose-sensitive X chromosome numerator elements those include genes such as sis-asis-brunt and less so sis-c and the autosomal denominators such as dpn in conjunction with the maternally derived products of the da gene and the more recently studied emcgroucho, her and snf see Figure 4 [ 12 ].
In mammals, sex determination is based on the presence of two identical XX or distinct XY gonosomes. We next explore whether this homology extends to the molecular level. Matsuda M: Sex determination in the teleost medaka, Oryzias latipes.
However, it has not yet been established whether the gene's product directly induces sex determination towards the female pathway, or rather acts a simple marker of this phenomenon, without active participation in the process per se [ 69 , 70 ].
Since reproduction is also the function that determines the categorization of specific populations in the same or different species, the analysis of the specific molecular patterns that this process may follow is crucial for the comprehension of the detailed biochemical background mediating and maintaining the phenotypical variety observed at a macroscopical level.
We now move from genes associated with ovary development to genes that may play a role in testis formation. Sex Determination Although the specific molecular mechanism that determines sex has not been revealed in any reptilian species, general modes of sex determination can be described [ Bull, ; Janzen and Paukstis, ].