During our review for our Cells and Diffusion we got some really great questions that I think have some interesting answers, but weren’t directly relevant to our review… so here is the second of four posts answering these questions.
Question 2: How does meiosis relate to identical twins?
The short answer to this is that meiosis doesn’t directly relate to identical twins, at least no more than it relates to the production of any other child.
Meiosis is the process by which eukaryotes create gametes (sex cells). We talked about in class how we need meiosis to halve the number of chromosomes in a sex cell (in comparison to a somatic cell) so that each generation doesn’t have a double in the number of chromosomes. Here’s a quick review:
The daughter cells of meiosis are the sex cells that come together to create a zygote. In the case of humans, one sperm (23 chromosomes) fertilizes one egg (also has 23 chromosomes) and the resulting zygote has the normal number of chromosomes (23+23=46). The zygote is a fertilized egg which after many rounds of division will develop into a fetus. For identical twins something a little different happens.. everything starts like with a single zygote, one sperm fertilizes one egg... but sometime very early in development, before you can even technically call the little ball of cells a fetus, it splits in half. The cells keeps dividing like they should and quickly make up for lost time, but the result is two identical fetuses. As far as scientists can tell, it is generally considered to be a spontaneous or random event to have identical twins, although it does seem somewhat more likely to occur in some families than others. Because the twins come from one zygote they are also called monozygotic twins.
For fraternal (non-identical) twins two eggs are fertilized by two different sperm. So you get two children who develop in the same womb and are born at the same time, but have different genetics. Because they come from two different zygotes, fraternal twins are also known as dizygotic twins. This means that each child can end up with very different genetics, like the twin girls pictured below!
For more information on the twins above check out this article by Justine Alford over at IFLScience.
