Iguanas Have Oldest Reptilian Sex Chromosome

By Laura Poppick, Staff Writer | March 04, 2014 07:01pm ET

Iguanas have the oldest known sex chromosomes in the reptilian world, according to a new report.

Sex chromosomes are the gene-carrying structures in cells that determine the sex of an organism. Some groups of animals, such as mammals and birds, pass down their sex chromosomes within evolutionary lineages and do not experience much variability as new species evolve through time. But other animals, such as reptiles, generally experience more genetic variability in sex chromosomes as new species evolve.

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Extra Girly Genes Boost Male Sex Drive

Women may not be known as the gender with the highest sex drive, but it turns out, at least in mice, males with an extra "girly" sex chromosome seemed to have an insatiable appetite for sex.

In mammals, gender is determined by "sex chromosomes," the X and Y. If you have two X chromosomes, you are a female. If you have one X and one Y, you are a male. (Chromosomes are long strings of DNA that hold many genes; humans have 23 pairs of chromosomes, one set inherited from each parent.)

The study was done in mice, not humans, but the genes that determine sex are similar in mammals, so the results might be applicable, especially in males with Klinefelter's syndrome, who are genetically XXY.

"Whether this is a specific phenomenon to mice, or even to this particular inbred background strain of laboratory mice, is still an open question, but we did find similar results in two different genetic models of mice," study researcher Paul Bonthuis, a graduate student at the University of Virginia, told LiveScience in an email. "To know how general the finding is to other mammals one would have to do studies with other mammalian species directly."

Read on:  http://www.livescience.com/19110-female-chromosome-male-sex.html