04/12/2023 1

Gametogenesis and fertilization

ByDr. Ansari

Chairperson & Prof. AnatomyRAKCODS. RAKMHSU

(for BDS students)

04/12/2023 2

The learning outcomes are

• The students are able to chart out the steps in Gametogenesis occurring in male persons and steps of oogenesis occurring in female subjects.

• The result of spermatogenesis and spermiognenesis.

• The result of oogenesis.• The fertilization is the result of union between

the male and female gametes occurring in the female reproductive organs.

04/12/2023 3

Formation of male gametes is called spermatogenesis

• It occurs in the testis of an adult male.• The mother cells are called as spermatogonia.• Each spermatogonium consists of 2n number of

chromosomes. • In human it is 46 chromosomes (22autosomes

and XX/XY sexosomes).• The supporting cells are called as sertoli cells.• They help in providing nutrition and helps in

spermiognenesis-maturation of sperms.

04/12/2023 4

There are three steps in spermatogenesis

• 1) Meiosis I, during which the number of chromosomes in the cell is reduced to half or 23 chromosomes each;

• 2) Meiosis II, during which each haploid cell forms spermatids; and

• 3) Spermiogenesis, during which each spermatid develops into a sperm cell with a head and tail.

• The entire process of spermatogenesis takes about 64 days.

04/12/2023 5

04/12/2023 6

The spermiogensis is regulated by Sertoli cells

7

The oogenesis occur in female reproductive organ- ovary

04/12/2023

04/12/2023 8

The fertilization is the union of male and female gametes-it occurs in uterine tubes

04/12/2023 9

04/12/2023 10

The result of fertilization• Stimulates the secondary oocyte to complete meiosis.

• Restores the normal diploid number of chromosomes (46).

• Results in variation of human species as maternal and paternal chromosomes intermingle.

• The embryo contains only maternal mitochondria because the sperm mitochondria are dispersed into the egg cytoplasm and discarded.

• Determines the sex of the embryo.

• The sex chromosome (Y or X) carried by the successful sperm determines embryonic sex.

• The sperm can only survive 48 hours within the female genital tract.

04/12/2023 11

Monozygotic twin

• A fertilized, single egg splits into two developing zygotes at a very early stage.

• Identical twins; same sex.

04/12/2023 12

Dizygotic twin:-

• Result from the fertilization by two sperms & two separate ova that have reached maturation at the same time.

• Not identical twins; can be different sexes

• Incidence increases with age of the mother

04/12/2023 13

Conjoint twins- Siamese twins

• Conjoint twins will result when the germ disk duplicates itself and will not get separated out at a particular point and remain joined.

• Whole two individuals will develop with parts attached with each other.

• Here it is a craniopagus.

04/12/2023 14

References

• http://education-portal.com/academy/lesson/oogenesis-how-the-female-reproductive-system-produces-eggs.html#lesson

• http://www.youtube.com/watch?v=BFrVmDgh4v4

• http://www.tutorsglobe.com/getanswer/process-of-fertilization-in-human-beings-908778.aspx