Twin
One of two children produced in the same pregnancy. Twins can develop from one ovum (egg) or from two ova (eggs). Twins who develop from a single ovum are called monozygotic or identical twins. They have identical genomes. Twins who develop from two ova that are fertilized at the same time are called dizygotic or fraternal twins. They are nonidentical and have different genomes.
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an involuntary contraction of a group of muscles, also known as a fasciculation.
- Twitching
Involuntary contractions of groups of muscle fibers. Also known as fasciculations. Fasciculations can occur in normal individuals without an associated disease or condition and can also occur as a result of illness, such as muscle cramps, nerve diseases, and metabolism imbalances.
- Two-animal rule
A rule instituted by the US Food and Drug Administration (FDA) for the licensing of agents directed against diseases of low or no incidence. The two-animal rule states that, when agents such as an antibiotic or vaccine are needed for such diseases, these agents may be licensed if they meet two criteria. One criterion is […]
- Two-faced twins
Known medically as diprosopus, two-faced twins are conjoined twins (incompletely separated identical twins). The twins have almost complete fusion of their bodies with one set of limbs. Part or all of the face is duplicated. The condition usually results in stillbirth. The ancient two-faced Mexican figurines known as the “pretty ladies of Tlatilco” are now […]
- TXA2
Thromboxane A2, the active form of thromboxane.