Two individuals from the same birth. May be monozygotic (identical) or dizygotic (fraternal).
One of two babies born to a mother at the same time.
Either of two offspring born at the same time from the same pregnancy. Twins may result from a single fertilized ovum that divides early in development to form two separate embryos (monozygotic— identical twins) or from two ova fertilized at the same time (dizygotic—fraternal twins).
Two siblings resulting from the same pregnancy. Twins occur in about 1 percent of all births. Most twins are fraternal, meaning that each baby developed from a separate egg and sperm and has its own placenta and amniotic sac. Fraternal twins can be the same sex or different sexes, and they may not look alike. Identical twins are rare, occurring when one fertilized egg splits early in pregnancy and develops into two fetuses. Identical twins may share a single placenta, but each fetus usually has its own amniotic sac. They are always the same sex, with the same blood type, and they always look alike, with the same hair and eye colors.
Two individuals who are born at the same time and of the same parents. Fraternal (or dizygotic) twins are the result of the simultaneous fertilization of two egg cells; they may be of different sexes and are no more alike than ordinary siblings, Identical (or monozygotic) twins result from the fertilization of a single egg cell that subsequently divides to give two separate fetuses. They are of the same sex and other-wise genetically identical; any differences in their appearance are due to environmental influences.
One of two children developed within the uterus at the same time from the same pregnancy.
The study of which, particularly using identical twins, affords a way of separating the effects of nature and nurture.
The use of identical twin studies by scientists in several disciplines has proved an effective way of distinguishing between possible causes. The most well known of these is the attempt to separate nature and nurture in intelligence. Do identical twins, separated at birth and brought up in different environments and cultures, nevertheless score the same IQ when tested years later? Or have their intelligences developed differently because of their different circumstances and the cultural influences on them? The jury is still out and advocates of both sides dispute the significance of the evidence, sometimes bitterly.
Two children born from a single pregnancy. Twins can arise from either a solitary egg or from two separate eggs.
Monozygotic, also known as identical, twins emerge when a lone fertilized egg splits during its initial phases of growth. If the egg doesn’t fully divide, conjoined twins are the outcome. Monozygotic twins share a common placenta. Even though one may frequently outweigh the other during birth, they invariably share the same gender and bear an astonishingly similar appearance.
Dizygotic, or fraternal, twins come into existence when two eggs are fertilized concurrently. The eggs they originate from might be discharged by either the same or distinct ovaries; the fertilization takes place simultaneously. Each of them possesses an individual placenta and could belong to distinct genders, exhibiting noticeable dissimilarities in their appearance.
Roughly one in 80 pregnancies results in twins.
Twins are two babies born from the same pregnancy.