Question

What are the events which lead to the formation of (a) identical twins, and (b) fraternal twins?

Answer 1

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.

Explanation:

Identical twins:

• 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.

Fraternal twins:

• 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.