Some lizards that begin to develop as males hatch into females if the egg is warm – and now scientists know why. Heat triggers genes that override chromosome sex determination.
In the 1960s, French scientists discovered that reptiles in Senegal are completely temperature-dependent during their development. For example, in Australia’s bearded lizards, sex determination depends on both genetics and the temperature of the environment. Males have two identical sex chromosomes – ZZ, and females have two different sex chromosomes ZW. But male embryos will develop like female embryos if the egg is warm enough. This means that women can develop in two ways, but the mechanisms that underlie this phenomenon have eluded scientists for more than half a century.
To solve the mystery, Sarah Whiteley of the University of Canberra in Australia and her colleagues performed genetic sequencing on unhatched bearded lizards incubated at either 28 ° C – cool enough for ZZ embryos to hatch into males, or 36 ° C – warm enough for ZZ to emerge. – female.
It turned out that at a temperature of 36 ° C, ZW female embryos had “sharply” different active genes at the main stages of sexual development compared to ZZ females. There are two different sets of genes that give rise to a female bearded lizard. In ZZ females, genes that “wanted” to code for male development were forcibly turned off, and genes for female development were turned on.