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Old 02-19-2012, 12:57 AM   #106
Warren_Booth
Helenthereef: snakes fo not have X and Y sex chromosomes. Instead, they have Z and W. Unlike mammals were males are the heterogametic sex (I.e. XY) in snakes females are heterogametic with ZW sex chromosomes. Males are ZZ. As a result true clonal females can only result from pre-meiotic doubling of chromosomes or apomoxis. This is known only from one case in Burmese pythons. I have produced the first and only papers of parthenogenesis in boas (Boa constrictor and Colombian rainbows). These produced females that have 2 W sex chromosomes as a result of one set if the females chromosomes being replicated, therefore resulting in a half clone of the mother. In the Caenophidians the males result from a doubling of one set of chromosomes with the Z chromosome duplicated. Why these produced makes and not females is unknown but likely a result of size variation in the sex chromosomes in the advanced snakes while Boidae and Pythonids have similar sized sex chromosomes.
Warren