FNR 24000 Lecture Notes - Lecture 21: Sex-Determination System, Gonadal Ridge, Exaptation
24 Oct 2018
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Most species, including many reptiles, have genotypic sex determination (gsd, sex chromosomes) Two types of gsd: and y sex chromosomes with females being homogametic (xx) and males heterogametic (xy, z and w sex chromosomes with males being homogametic (zz) and females heterogametic (zw) However, this is not the only way that sex is determined in reptiles. Sex can also be determined by the environmental conditions that occur during embryonic development. In temperature-dependent sex determination (tsd), incubation temperature determines whether an egg develops as male or female. The thermosensitive period occurs after the egg has been laid so sex is at the mercy of the ambient conditions affecting egg clutches in nests. Tsd is found in some lizards, turtles, and crocodilians. Hoe does the physical stimulus of temperature alter sex. Temperature alters physiological and molecular signals that determine the type od gonad that will be formed. Temperature activates genes that encode for steroidogenic enzymes. The enzyme aromatase converts testosterone into estrogen.
