GENERAL HISTOLOGY

Detailed explanation-1: -To form identical or monozygotic twins, one fertilised egg (ovum) splits and develops into two babies with exactly the same genetic information. To form fraternal or dizygotic twins, two eggs (ova) are fertilised by two sperm and produce two genetically unique children.

Detailed explanation-2: -1 As the fertilized egg (called a zygote) travels to the uterus, the cells divide and grow into a blastocyst. In the case of monozygotic twins, the blastocyst then splits and develops into two embryos. In contrast, dizygotic (fraternal) twins form when two separate eggs are released and fertilized by two sperm.

Detailed explanation-3: -Identical twins (also called monozygotic twins) result from the fertilization of a single egg by a single sperm, with the fertilized egg then splitting into two. Identical twins share the same genomes and are always of the same sex.

Detailed explanation-4: -If more than one sperm fuses-a condition called polyspermy-multipolar or extra mitotic spindles are formed, resulting in faulty segregation of chromosomes during cell division; nondiploid cells are produced, and development usually stops. Two mechanisms can operate to ensure that only one sperm fertilizes the egg.

Detailed explanation-5: -Monozygotic twinning (MZT) occurs when an embryo splits after fertilization, resulting in identical twins. The incidence of MZT is 0.42% naturally (in normal pregnancies).