What are the events which lead to the formation of (a) identical twins, and (b) fraternal twins?
Fraternal twins occur when the female produces two eggs and identical twins occur when the female produces one egg and the zygote spontaneous divides into two.
- In this case, the zygote undergoes cleavage(cell division by mitosis) when embryo is at two-celled stage.
- The two blastomeres may separate and then each behave as an independent zygote.
- Thus each broken blastomere give rise to a new independent individual.
- As both the organisms are produced as a result of mitosis, both have identical genetic makeup and are called identical twins.
- These twins involve sort of asexual reproduction after the normal sexual reproduction.
- Identical twins can't be of different genders. Mean both will be either males or females.
In some exceptional cases, the female produces more than one eggs.
All eggs are independently fertilized by sperm.
So, they form two or more zygotes. Each zygote develops into a new offspring.
These offspring have different genetic combinations.
They may be two or more than two. Such offspring are called fraternal twins or triplets.
They are produced sexually.
Fraternal twins can have different genders as they don't have same genetic recombination.