They concluded this upon observing that mice without jagged-2 have a significant increase in hair cell density, compared with normal mice. Kelley and colleagues also observed that jagged-2 is expressed by nascent hair cells of normal mice whereas Notch is expressed in supporting cells. Because the Drosophila counterparts of Notch and jagged-2 have been demonstrated to mediate sensory bristle development, it has been suggested that the Drosophila bristle and the mammalian ear share a common evolutionary origin. But as he also notes, it is nonetheless satisfying to get at one of the roots of the magnificent mechanosensory mosaic comprised by the inner-ear hair cells. Since then, their 'sex' chromosomes have diverged to the extent that each species appears to have a different system for determining sex.
Human females have two 'X' sex chromosomes, and are therefore called the homogametic sex.
Human males have an 'X' and a 'Y' sex chromosome, making them the heterogametic sex. In contrast with the human condition, the genetic determination of sex in birds is obscure. Human and chicken versions of DMRT1 lie within this region. Other studies have shown that human DMRT1 is expressed in the testes and its structure is similar to sex-regulatory genes in flies and worms. While it's clear that sex isn't just for the birds, birds may end up telling us something about sex.