Rachel Sokol. Two OB-GYNs explain how common it is to birth twins and some interesting facts about twins in general. Do twins skip a generation? Why is it that many women who undergo IVF end up with twins? Is that just a coincidence? What are the chances of conceiving twins naturally?
Is it just me, or just it seem like there are so many twins around lately? If a man has inherited the hyperovulation gene from his mother, he may pass this gene on to his daughter, but it won't impact on the chances of him conceiving multiples with his own partner.
Men, of course, don't ovulate, so the chance of twins or more is up to the woman. The man's daughter, however, having inherited the hyperovulation gene through her father is then more likely to release more than one egg when she ovulates and therefore could conceive fraternal twins.
In that scenario, it would seem as though the twins have, in essence, skipped a generation. Identical twinning and family heredity Identical twins happen when a single embryo splits in two soon after fertilisation.
Do twins skip a generation? AMBA Sponsor. Media Releases Casting Calls. Compared with the general population, women with a mother or sister who have had DZ twins are about twice as likely to have DZ twins themselves. DZ twinning is thought to be a result of hyperovulation, which is the release of more than one egg in a single menstrual cycle. To explain how DZ twinning can run in families, researchers have looked for genetic factors that increase the chance of hyperovulation.
However, studies examining the contributions of specific genes have had mixed and conflicting results. Few specific genes in humans have been definitively linked with hyperovulation or an increased probability of DZ twinning.
Assisted reproductive technologies such as in vitro fertilization IVF are also associated with an increased frequency of DZ twins. Dizygotic twinning. Hum Reprod Update. Epub Nov PubMed: Machin G. Familial monozygotic twinning: a report of seven pedigrees. This is why the DNA of fraternal twins is different. Usually, a woman only releases a single egg at a time. Fraternal twins can only happen if a mother releases two eggs in one cycle.
This is called hyperovulation. Unlike embryo splitting, ovulation is a normal biological process that is controlled by our genes. And, different women can have different versions of these ovulation genes.
Some women have versions called alleles of these genes that make them more likely to hyperovulate. This means there is a higher chance that two eggs could get fertilized at once, leading to fraternal twins. The gene versions that increase the chance of hyperovulation can be passed down from parent to child. This is why fraternal twins run in families. We went over a lot of this stuff in our previous answer, but your question got me thinking.
Our last answer on twins was done so long ago. Has recent research discovered anything new on this fascinating topic? They have indeed… at least if you are a sheep! Scientists often turn to animals when they want to study a biological process. Some of the newest information we have about twin genetics comes from studying sheep. Sheep were chosen because, like people, they typically give birth to a single lamb.
However, they can sometimes have twins and triplets. Different breeds of sheep naturally have higher or lower twin rates. These different breeds have different versions called alleles of some of their genes. Specific alleles can make certain breeds more likely to have twins.
We can compare the genes between these different breeds to try to find the genes controlling twinning. And, this is just what scientists did. A thorough search for genes controlling twining in sheep identified several interesting ones.
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