Mammalian Female
A distinguishing characteristic of the class Mammalia is the presence of mammary glands. The mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals produce milk. Mammary glands are most obvious in humans, as the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent breasts. Today some human females also surgically augment their breast size. However, mammary glands are present in all mammals, although they are vestigial in the male of the species.
The mammalian female has two copies of the X chromosome as opposed to the male which carries only one X and one smaller Y chromosome. To compensate for the difference in size, one of the female's X chromosomes is randomly inactivated in each cell. In birds and reptiles, by contrast, it is the female who is heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes.
Mammalian females bear live young (with the rare exception of monotremes, which lay eggs). Some non-mammalian species, such as guppies, have analogous reproductive structures; and some other non-mammals, such as sharks, whose eggs hatch inside their bodies, also have the appearance of bearing live young.
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Famous quotes containing the words mammalian and/or female:
“Specialization is a feature of every complex organization, be it social or natural, a school system, garden, book, or mammalian body.”
—Catharine R. Stimpson (b. 1936)
“The elephant, not only the largest but the most intelligent of animals, provides us with an excellent example. It is faithful and tenderly loving to the female of its choice, mating only every third year and then for no more than five days, and so secretly as never to be seen, until, on the sixth day, it appears and goes at once to wash its whole body in the river, unwilling to return to the herd until thus purified. Such good and modest habits are an example to husband and wife.”
—St. Francis De Sales (1567–1622)