An “Intersex” whale? Nearly all mammals use the XX/XY chromosomal system of sex determination, where females carry two X chromosomes and males carry XY. (In contrast, birds use the ZW system, in which males have two of the same sex chromosomes.) Last fall, a fascinating study documented the first case of an XXY chromosomal aneuploidy in a southern right whale. Differences in chromosome number are called aneuploidies, and this particular whale has what’s known as Klinefelter’s. News reports, howe

1.6M views · 60K reactions | Although XX and XY are definitely the...