Twin
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A twin is one of two animals that are both from the same pregnancy. Human twins are two people that shared the uterus during a single pregnancy, and one is normally born quickly after the first. Because of the size of the uterus, multiple pregnancies are less likely to last the full 38 weeks than most single birth pregnancies.
There are five variations of twinning that occur commonly in the world. The three most common variations are all fraternal, meaning the two twins are not from the same egg: (1) male-female twins are the most common result, at about 40% of all twins born; (2) female fraternal twins (sometimes called sororal twins); (3) male fraternal twins. The last two are identical: (4) female identical twins and (5) (least common) male identical twins.
Twinning is common in many other animals, such as cats, sheep, and ferrets. Twinning occurs in cattle about 1-4% of the time, and research is underway to improve the odds of twinning, which can be more profitable for the breeder if complications can be sidestepped or managed.
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