According to conventional wisdom, twins not only run in families, but they also — for some strange reason — always skip at least one generation.
Many people believe twins skip a generation, but that's just a myth. The idea that twins skip generations likely comes from the fact that the genetic factors contributing to twins only come from the gestational parent's side.
It's a common misconception that twins skip a generation in families. There is absolutely no evidence, other than circumstantial, that twins are more likely to occur every other generation.
However, for a given pregnancy, only the mother's genetics matter. Fraternal twins happen when two eggs are simultaneously fertilized instead of just one. A father's genes can't make a woman release two eggs.
The quick answer to this question is that, in a twin pregnancy, it is the mother's genes that determine twins. First up, giving birth to identical twins is not genetic, but conceiving fraternal twins is. The mother may have the genetic trait of releasing two eggs in one menstrual cycle.
Factors that increase the chance of twins include: consuming high amounts of dairy foods, being over the age of 30, and conceiving while breastfeeding. Many fertility drugs including Clomid, Gonal-F, and Follistim also increase the odds of a twin pregnancy.
Some research has found that having fraternal twins in a mother's immediate family may double the chances of conceiving fraternal twins. One theory is that it's because a certain gene may predispose some women to "hyperovulation," or releasing more than one egg during each menstrual cycle.
When both eggs are fertilized, the resulting siblings are fraternal twins. Because this gene can be passed on, the tendency to have fraternal twins can in fact run in families. Identical twins, on the other hand, result from one fertilized egg randomly splitting in two, creating two siblings with identical DNA.
Identical twins have 100% of their DNA the same while fraternal twins share only 50%. But what about semi-identical twins? Well, they have 75% of their DNA the same.
Identical twins form from the same egg and get the same genetic material from their parents — but that doesn't mean they're genetically identical by the time they're born.
If you're pregnant, you're about twice as likely than average to be expecting twins if you're a non-identical twin, or have siblings who are non-identical twins .
Recessive traits like red hair can skip generations because they can hide out in a carrier behind a dominant trait. The recessive trait needs another carrier and a bit of luck to be seen.
Everyone has the same chance of having identical twins: about 1 in 250. Identical twins do not run in families. But there are some factors that make having non-identical twins more likely: non-identical twins are more common in some ethnic groups, with the highest rate among Nigerians and the lowest among Japanese.
When people refer to Irish twins, it's important to recognize that although the siblings are close in age, they are not actually twins. In other words, they were not born during the same gestational period. Calling them Irish twins is just an informal way of classifying siblings that are born close together.
In 99.9% of cases boy/girl twins are non-identical. However, in some extremely rare cases resulting from a genetic mutation, identical twins from an egg and sperm which began as male (XY) can develop into a male / female pair.
According to The American Society for Reproductive Medicine, women who are fraternal twins have a 1 in 60 chance of having twins, and men who are fraternal twins have a 1 in 125 chance of fathering twins. It was previously believed that identical (monozygotic) twins were random — not genetic.
They come from the same fertilized egg and share the same genetic blueprint. To a standard DNA test, they are indistinguishable. But any forensics expert will tell you that there is at least one surefire way to tell them apart: identical twins do not have matching fingerprints.
Is there a third type? Traditionally, the science around twins has taught that identical and fraternal are the only two types. But a third type might exist, called polar body or half-identical twins.
Identical twins will always have the same blood type because they were created from the same fertilized egg (fraternal twins can have different blood types — again, providing the parents do — because they are created by two fertilized eggs).
The National Organization of Mothers of Twins Clubs claims that once you have had fraternal (dizygotic) twins, your chances of having another set are three to four times greater than that of the general population. Both hereditary and environmental factors may contribute to this.
Having two babies at a time is associated with a longer life, according to a new study. But that's not because doubling up on dirty diapers increases life span; instead, moms of twins are physically stronger in the first place.
It's estimated that 1 in 250 pregnancies results in twins naturally, and there are two ways to conceive them.
A big reason for all those twins is an increase in medically assisted reproduction, including in vitro fertilization, ovarian stimulation and artificial insemination. Another reason is that women in many countries are having babies at older ages.