This section of notes introduces the X chromosome and its role in development. There is a separate page discussing X chromosome inactivationt that has to occur in female development to provide the correct gene dosage.
X Chromosome Overview
Snake species have genetic sex determination by the ZZ/ZW type of sex chromosomes (mammals XX/XY sex chromosomes). A recent study has investigated the origins of these sex chromosomes. Matsubara K, Tarui H, Toriba M, Yamada K, Nishida-Umehara C, Agata K, Matsuda Y. Evidence for different origin of sex chromosomes in snakes, birds, and mammals and step-wise differentiation of snake sex chromosomes. Proc Natl Acad Sci U S A. 2006 Nov 16
"All human and chicken homologues of the snake Z-linked genes were located on autosomes, suggesting that the sex chromosomes of snakes, mammals, and birds were all derived from different autosomal pairs of the common ancestor."
Human Embryology Movies: Female Gonadal Development (315Kb) | Formation of Uterus and Vagina (706Kb) | Male Genitalia Development (434 Kb) | Female Genitalia Development (357Kb)
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The male and female reproductive systems develop initially "indifferently", it is the product of the Y chromosome SRY gene that makes the difference.
Please email Dr Mark Hill if you wish to make a comment about this current project.