Probability of identical twins

Identical twins are a rare event, with a probability of 4 in 1,000. Identical twins mean that the fertilized egg splits into two embryos and develops, and the genetic material of these two embryos is the same. Children born from identical twins have the same appearance and gender. However, there is a difference between the two compared to twins born from identical twins, who are born from the fertilization of two eggs.

The probability of having identical twins is about 4 in 1,000.

Identical twins are twins that are formed when one sperm and one egg combine to form a single fertilized egg. The fertilized egg splits into two, forming two embryos. Because they come from the same fertilized egg, they receive exactly the same chromosomes and genetic material. The probability of identical twins occurring does not change with race, genetics or environment, and is approximately 4/1000; in addition, if the mother or her family has given birth to twins, it is more likely to conceive twins, so the mother's genetic influence may be more important than the father's. So, the probability of having identical twins is about 4/1000.

2 What is the probability of having fraternal twins?

The probability of having fraternal twins varies from person to person.

Fraternal twins can be the same sex or different sexes. Because fraternal twins result from multiple ovulation, their numbers have been higher in recent years, especially with the increased use of fertility drugs, which facilitate multiple ovulation. Approximately 4 in every 1,000 births are identical twins, but fraternal twins occur at different rates in different ethnic groups and at different maternal ages. Young women (under 20) rarely have fraternal twins (about 3 per 1,000 births), while women aged 35 to 40 have fraternal twins about 14 per 1,000 births. Asians rarely have fraternal twins, while blacks have the most.

Therefore, the probability of having fraternal twins varies from person to person.

Are identical twins more likely to occur or fraternal twins more likely to occur?

The probability of identical twins is higher.

The probability of identical eggs is high. Because when a mother ovulates, she usually releases one egg, and then two sperm enter the egg at the same time and become a fertilized egg. If the Y chromosome carried by the sperm combines with the X chromosome of the egg, the resulting embryo is a male. If the X chromosome carried by the sperm combines with the X chromosome of the egg, the resulting embryo is a female.

Then if the mother releases two eggs during ovulation, the probability is relatively small, and it is also possible to give birth to twins, that is, the two eggs are fertilized at the same time and develop into embryos separately. The twins may not look very similar. It should be said that they are just brothers and sisters born in the same time period.