Q:

How are non-identical twins made?

A:

Quick Answer

Nonidentical twins occur when a woman produces two separate eggs that are then fertilized by two different sperm cells. The resulting twins sometimes look alike, but have separate genetic identities, like children of the same parents born during different pregnancies. Another name for nonidentical twins is fraternal twins.

Know More
How are non-identical twins made?
Credit: UIG via Getty Images Universal Images Group Getty Images

Full Answer

Nonidentical twins only form when two eggs release during the same ovulation. In some cases, the eggs release simultaneously. In others, the ovaries initially release one egg. After fertilization that egg begins moving to the uterus to attach. The ovaries then release a second egg, fertilized by a later act of sexual intercourse. This leads to the potential of a woman giving birth to nonidentical twins with two separate fathers. In this case, the genetic identity of the twins is the same as a half-sibling born from separate pregnancies.

The sex of fraternal twins has a chance of differing. Identical twins develop when a single egg fertilized by a single sperm splits to form two different babies. These twins have the same genetic identity. Identical twins are always the same sex.

While some women produce multiple eggs with every ovulation, others begin producing multiple eggs as they grow older. Genetics also plays a role in the chance of conceiving twins. Use of fertility drugs increases the chance of producing more than one egg during each cycle.


Is this answer helpful?

Similar Questions

  • Q:

    What are dizygotic twins?

    A:

    Dizygotic twins, also known as heterologous or fraternal twins, develop when two separate eggs are fertilized at the same time within the uterus. Dizygotic twins do not have identical genetics and can be of the same sex or of the opposite sex.

    Full Answer >
    Filed Under:
  • Q:

    What does "fraternal twins" mean?

    A:

    Fraternal twins, also known as dizygotic twins, occur when two separate eggs are fertilized by two separate sperm. This results in two babies who are not identical and who do not come from the same egg. Fraternal twins can consist of two girls, two boys or one girl and one boy.

    Full Answer >
    Filed Under:
  • Q:

    What causes Siamese twins?

    A:

    The exact cause of Siamese twins, more accurately known as conjoined twins, is not entirely known. Since the prevalence of conjoined twins is thought to be higher in southeast Asian and African populations than in Caucasian populations, Sciences 360 suggests that environmental or genetic factors may play some role in the formation of conjoined twins.

    Full Answer >
    Filed Under:
  • Q:

    What is the difference between paternal and maternal twins?

    A:

    Paternal and maternal twins, commonly known as fraternal and identical twins, are distinguished by the different ways the multiple pregnancy begins. Identical twins begin as a single zygote that splits into two or more developing embryos. Fraternal twins are usually the result of multiple eggs being present for fertilization.

    Full Answer >
    Filed Under:

Explore