Wednesday, April 22, 2015

How are twins produced? Do they have 46 chromosomes each?

Yes. Individuals that are twins have 46 chromosomes. Twins can be either identical or fraternal. Identical twins have the same exact DNA, whereas fraternal twins do not. The production of each type of twin is briefly explained below.


Identical twins


Identical twins are also called monozygotic twins because they come from a single zygote (“mono” = one, “zygotic” =  zygote, or fertilized egg). Identical twins both come from the same egg that is fertilized by a single sperm.  When the fertilized egg is still a small clump of cells, it divides into two. Each half then develops into two babies.


Fraternal twins  


Fraternal twins are sometimes called dizygotic twins because they come from two different fertilized eggs (“di” = two, “zygotic” = zygote, or fertilized egg).  Two eggs are released during the ovulation cycle of a female. Each egg is then fertilized by two different sperm. Thus, two different individuals form at the same time within a single womb.

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