twin

Twins are two offspring produced by the same *******cy. Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic ('non-identical' or 'fraternal'), meaning that each twin develops from a separate egg and each egg is fertilized by its own ***** cell. Since identical twins develop from one zygote, they will share the same ***, while fraternal twins may or may not. In rare cases twins can have the same mother and different fathers (heteropaternal superfecundation).
In contrast, a fetus that develops alone in the womb (the much more common case, in humans) is called a singleton, and the general term for one offspring of a multiple birth is a multiple. Unrelated look-alikes whose resemblance parallels that of twins are referred to as doppelgängers.

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