fraternal twins

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di·zy·got·ic twins

twins derived from two zygotes.

fraternal twins

fraternal twins

Dizygotic twins Twins resulting from 2 separate fertilized eggs liberated simultaneously from the ovaries that develop in separate or partially fused chorionic sacs; 70-80% of twins are dizygotic. Cf Identical twins.

di·zy·got·ic twins

(dī-zī-got'ik twinz)
Twins derived from two zygotes.
Synonym(s): fraternal twins, heterologous twins.


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TWINS: A. Monozygotic twins with one placenta, one chorion, and two amnions. B. Dizygotic twins with two placentas, two chorions, and two amnions
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TWINS: A. Monozygotic twins with one placenta, one chorion, and two amnions. B. Dizygotic twins with two placentas, two chorions, and two amnions
One of two infants born sharing some common anatomical parts. See: illustration; fetus papyraceus; Hellin's law


Per 1000 live births, incidence rates for American whites are 1:88; for American blacks, 1:70. Generally, the rates are higher in blacks and East Indians and lower in Northern Europeans.

Research on Twins

Identical and fraternal twins provide a unique resource for investigating the origin and natural history of various diseases and discovering the different rates of environmental and hereditary factors in causing physical and mental disorders. Esp. important are studies that follow the course of identical twins separated shortly after birth and who then grew up in different social, economic, educational, and environmental conditions. In other research, the second-born twin was found to be at increased risk for an unfavorable outcome (e.g., need for intubation and resuscitation, lower 5-min Apgar score), even when delivered by cesarean section.

biovular twins

Dizygotic twins.

conjoined twins

Twins that are united. In some cases, the individuals are joined in a small area and are capable of activity, but the extent of union may be so great that survival is impossible.

dizygotic twins

Twins from two separate, fertilized ova. Synonym: biovular twins; fraternal twins

enzygotic twins

Monozygotic twins.

fraternal twins

Dizygotic twins.

growth discordant twins

The unequal growth of twins while in utero. The smaller twin is at greater risk of having congenital anomalies than is the normal birth-weight twin.
Synonym: unequal twins

identical twins

Monozygotic twins.

impacted twins

Twins so entwined in utero as to prevent normal delivery.

interlocked twins

Twins in which the neck of one becomes interlocked with the head of the other, making vaginal delivery impossible.

monozygotic twins

Twins that develop from a single fertilized ovum. Monozygotic twins have the same genetic makeup and, consequently, are of the same gender and strikingly resemble each other physically, physiologically, and mentally. They develop within a common chorionic sac and have a common placenta. Each usually develops its own amnion and umbilical cord. Such twins may result from development of two inner cell masses within a blastocyst, development of two embryonic axes on a single blastoderm, or the division of a single embryonic axis into two centers.
Synonym: enzygotic twins; identical twins; true twins; uniovular twins

parasitic twin

The smaller of a pair of conjoined twins, when there is a marked disparity in size.

Siamese twins

A culturally insensitive term for conjoined twins.
See: conjoined twin

true twins

Monozygotic twins.

unequal twins

Growth discordant twins.

uniovular twins

Monozygotic twins.

vanishing twin

Fetal resorption in multiple gestation.
See: gestation, multiple

fraternal twins

Non-identical twins produced by the simultaneous fertilization of two different eggs by different sperms (dizygotic twins). In spite of the etymology, fraternal twins need not be male or even of the same sex.

fraternal twins

References in periodicals archive ?
And fraternal twins are more alike than virtual twins.
Further, an apparently single placenta may be present with fraternal twins.
Concordance rates are in the upper 20% range for fraternal twins.
The chances of any couple having fraternal twins is about 1 in 100 births, Austin said.
In a transplant between fraternal twins, he then performed the first successful transplant against the immune barrier.
For example, identical twins share 100 percent of their genes, fraternal twins and other full siblings share on average 50 percent of their genes, and unrelated people reared together (e.
Jim and Kate, fraternal twins and middle children, embraced the duties of running a public company.
She had had two pregnancies, both of which culminated in cesarean sections; during one of them, she delivered fraternal twins.
By comparing the incidence of cancer in identical twins (who share all the same genes) to fraternal twins (who, like most siblings, share an average of 50 percent of their genes), the researchers estimated what percent of the cancers were hereditary.
Twins tended to share responses to the cartoons, but identical twins were no more likely to hit the same mark on the funny meter than were fraternal twins, who share only half their genes.
For example, autism, attention deficit/hyperactivity disorder, and multiple sclerosis occur more frequently in identical twins than in fraternal twins, suggesting an underlying genetic susceptibility in these disorders (15-17).
The first studies of identical and fraternal twins, begun in this decade, extended knowledge about the genetics of MS.