Gametogenesis in Humans



Gametogenesis in Humans

  1. Process of gamete formation is known as gametogenesis
  2. Gametogenesis that involved sperm formation is known as spermatogenesis, whereas those involved ovum formation is known as oogenesis

Necessity of gametogenesis:

  • Produces gametes and haploid chromosomal number through meiosis
  • Produces genetic variation in gametes
  • Maintains diploid chromosomal number of zygote
  • Produces genetic variation in offspring
  • During foetus development, primordial germ cells divide mitocially to form spermatogonia
  1. Each spermatogonia (2n) grows and develops into primary spermatocytes (2n)
  2. Each primary spermatocyte (2n) divides by meiosis I to form tqo secondary spermatocytes (n)
  3. Each secondary spermatocyte (n) divides by meiosis II to form two spermatids (n)
  4. Each spermatid (n) undergoes differentiation to form sperm (n)
  • The sperms formed move to epididymis to be matured
  • Head of sperm contains nucleus and acrosome. The nucleus contains chromosomes and the acrosome contains enzymes for fertilisation.
  • Midpiece of sperm contains abundant of mitochondria to produce more energy for movement
  • The tail helps sperm to move
  • During foetus development, primordial germ cells divide mitotically to form oogonia
  • Polar body formed has size much smaller than secondary oocyte or ovum
  • The three polar bodies will degenerate and do not take part in fertilisation
  • At first, primary oocyte that surrounded by follicle cells is known as primary follicle
  • At puberty, follicle stimulating hormone (FSH) secreted by pituitary gland stimulates the development of follicle in ovary
  • Follicle cells start to divide by mitosis during development of follicle. The primary follicle developed into secondary follicle and then into a mature follicle,graafian follicle
  • During the follicle development, primary oocyte undergoes meiosis I to form secondary oocyte.
  1. At foetal stage, the primordial germ cells divide repeatedly by mitosis to form many diploid oogonium (2n)
  2. Each oogonium grows ad develops to form primary oocyte (2n). Each primary oocyte is surrounded by a layer of follicle cells to form a primary follicle.
  3. Before birth, the primary oocytes undergoes an incomplete meiosis I until prophase I
  4. At puberty, one primary oocyte completes meiosis I to form a secondary oocyte (n) and a polar body (n). The haploid polar body formed also undergoes meiosis II to form another two haploid polar bodies
  5. Secondary oocyte is surrounded by follicle cells known as secondary follicle 
  6. Secondary follicle grows and matures to form graafian follicle which then moves to the surface of the ovarian wall
  7. Ovulation: The Grafiian follicle bursts and releases the secondary oocyte into Fallopian tube
  8. If fertilisation occurs, secondary oocyte completes meiosis II to form a polar body (n) and an ovum (n). All 3 polar bodies will degenerate.
Comparison between spermatogenesis and oogenesis:

Simillarities between spermatogenesis and oogenesis:

  • Occur in reproductive organs
  • Produce haploid gametes
  • Involved in fertilisation
Differences between spermatogenesis and oogenesis:
Aspects Spermatogenesis
Organ of gamete formation Testis
Gamete formed Sperm
Structure of gamete Head, midpiece and tail 
Ability to move Move with tail 
Presence of follicle cell No follicle cells surround the gamete
Number of gamete formed from one parent cell Four 
Formation of polar body None 
Size of gamete Small
Mitotic division on parent cell Occurs throughout life after puberty
Meiotic division during gamete formation Occurs continuously without a break
Differentiation Involves differentiation
Aspects Oogenesis
Organ of gamete formation Ovary
Gamete formed Ovum
Structure of gamete Spherical shape
Ability to move Assists by cilia in the Falllopian tube 
Presence of follicle cell Follicle cells surrounding the gamete
Number of gamete formed from one parent cell One
Formation of polar body One or three
Size of gamete Large
Mitotic division on parent cell Only occurs during foetal development stage
Meiotic division during gamete formation Occurs by stages reagrding to foetal,puberty and after fertilisation stage
Differentiation Does not involve differentiation