Snakes do not possess X and Y sex chromosomes. They have Z and W. Females are the heterogametic sex (i.e.ZW). Males on the other hand are ZZ. Futhermore, across snake lineage we see heteromorphism in the sex chromosomes. In the basal lineages (i.e. Boidae and Pythonidae) we see no size difference in the sex chromosomes, whereas in the more derived lineages we see size variation. What makes it further confusing is that the sex determination genes are known to exist on different chromosomes in different lineages. One last thing, the mode of parthenogenesis used across different lineages varies, therefore in some we see terminal fusion automixis. This essentially results in half clones of the mother, therefore the parthenogens can either be ZZ (male) or WW (female). This later arrangement was considered not viable until my research in 2011 on Boids. THe former results in males. This form is considered employed the boidae resulting in WW females, and in the Caenophidians, resulting in ZZ males. In the Pythonids, they appear to use a different mode which essentially results in clones of the mother, and thus ZW. So, all things combined results in variation in the sex and chromosomal arrangement/level of heterozygosity across the genome in different snake lineages. Its not simply a case of all parthenogens are female.

Warren
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Dr Warren Booth / Director USARK
North Carolina State University
Department of Entomology

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