Verified by What Are Fraternal Twins?
Fraternal or dizygotic twins develop from two different eggs fertilized by separate sperm; they generally share about 50 percent of their genes. Therefore, fraternal twins are essentially like typical brothers and sisters. Similarities found between sets of fraternal twins suggest that the environment can influence traits greatly.
About 23 in every 1000 births are fraternal, a much higher rate than the three or four out of 1000 births for identical twins. Examining each twin’s DNA will reveal whether they are identical or fraternal; fraternals also normally have separate amniotic sacs, as well as separate placentas.
Yes. Identical twins share the same gender—boy-boy, girl-girl. Boy-girl twins are always fraternal. A boy-girl pair may be identical with a rare genetic mutation, but this brother and sister are like regular siblings born together.
Fraternal twins can look alike as much as two siblings can look alike. Again, fraternal twins are not identical and do not share the same chromosomes and genes.
When a woman hyperovulates, or releases more than one egg, then has sex with multiple partners, this could result in twins who have different fathers. One egg is fertilized by one man, another egg by the second man. This is called superfecundation.
Mixed-gender twins are the most common type of fraternals, some 50 percent are boy-girl. To understand this combination: Males have XY chromosomes, females have XX chromosomes. You have a girl twin when the father’s X chromosome combines with the mother’s X chromosome. You have a boy twin when the father’s Y chromosome combines with the mother’s X chromosome. The father determines gender.
A woman who is a fraternal twin, indeed has a greater chance of giving birth to fraternal twins. The odds of having fraternal twins are doubled, in fact, if the mother has fraternal twins in her immediate family.
No. Fraternal twins come from two separate eggs, and they each have their own placentas. However, in some instances, the two placentas can merge and form into one.
In a normal pregnancy, the ovaries halt the release of eggs. Yet in some pregnancies, the ovaries continue to release additional eggs, which is then impregnated by sperm. Therein, you have a womb with two embryos of different ages. This process is called superfetation. These are not fraternal twins, fraternal embryos are the same age.
Once an egg is fertilized, two layers are formed to prevent additional sperm from entering. Sometimes, in rare cases, additional sperm can enter an egg, which results in a triploid offspring, not twins. This embryo has an extra set of chromosomes, totaling 69; the normal number is 46. Triploid infants are commonly miscarried or stillborn; those born alive do not live more than a few hours or days after birth.
