Egg temp & gender probabilities

[Pythonfriend]

pythons have sex-determining chromosomes.

in humans, men have "XY" and women have "XX", and half of the children will get the Y-chromosome, and its determined at the moment of fertilization.

its similar in pythons, except that the roles of the genders are the other way around. so we use different letters, to avoid confusion. males have "ZZ" and females have "ZW". half of the unfertilized follicles get "W", the other half gets "Z". when they get fertilized and each follicle gets another "Z", the gender is already determined.

its not like this in all reptiles, many reptiles do not have this mechanism.

i found this paper, it doesnt specifically mention pythons, but it really explains it all:

http://www.plosbiology.org/article/i...l.pbio.1001643

Sex chromosomes have evolved from non-sex-determining chromosomes (autosomes) multiple times throughout the tree of life. In snakes, females are the heterogametic sex, in that they have two different sex chromosomes, Z and W, while males have two Z chromosomes. However, while in some snake species (e.g., boids) the Z and W chromosomes look identical (“homomorphic”), in others (e.g., vipers) they are very different in size and structure (“heteromorphic”); yet other species (e.g., colubrids) appear intermediate between these two states. This diversity makes snakes ideally suited for studying the evolutionary dynamics of sex chromosome differentiation.

i found other sources that specifically mention pythons. the species of reptiles where temperature is the deciding factor lack this mechanism, males and females have the same genetics, and the difference between the genders is that different genes are switched on or off. but when such a mechanism is in place, sex determination is entirely independent of outside influence, it all happens in the female long before the eggs are fully formed.