Gametogenesis is the process by which diploid precursor cells undergo meiotic division to become haploid gamete, but what are these processes? In this IBDP Biology blog, we will learn:
- What is Spermatogensis
- What is Oogensis
- Fertilization of two zygotes
Spermatogensis
This process occurs within males reproductive systems for the sperm within the testes
- Spermatogenesis describes the production of
- spermatozoa (sperm) in the seminiferous tubules of the testes
- The first stage of sperm production is the
- division of germline epithelium by mitosis
- These cells (spermatogonia) then undergo a period of
- growth
- This is followed by two meiotic divisions that result in
four haploid daughter cells
- These haploid cells then
differentiate to form sperm cells
- The developing sperm cells are
nourished throughout by the Sertoli cells
Oogensis
- The process begins during
- foetal development, when a large number of cells (oogonia) are formed by mitosis before undergoing a period of growth
- These cells begin meiosis but are arrested in
- prophase I until puberty
- At puberty, some follicles continue to develop each month is response to FSH secretion
- These follicles complete the first meiotic division to form two cells of unequal size
- The cell with less cytoplasm is a polar body (which degenerates), while the larger cell forms a secondary oocyte
- The secondary oocyte begins the second meiotic division but is arrested in
prophase II (until fertilisation)
- It is released from the ovary (ruptured follicle develops into corpus luteum) and, if fertilisation occurs, will complete meiosis
- The second meiotic division will produce an ovum and a second polar body
The male and female reproductive gametes (sperm and egg) have specialised structures which reflect their functions
- The male gamete (sperm) is small and motile and only contributes the male’s haploid nucleus to the zygote
- The female gamete (egg) is large and non-motile and contributes all the organelles and cytoplasm to the zygote
The process of Fertilisation
- The sperm is attracted to the egg due to the release of chemical signals from the secondary oocyte (
- chemotaxis)
- Fertilisation generally occurs in the oviduct (fallopian tube)
- To enter the egg membrane, the sperm must
- penetrate the protective jelly coat (zona pellucida) surrounding the egg via the acrosome reaction
- The acrosome vesicle
- fuses with the jelly coat and releases digestive enzymes which soften the glycoprotein matrix
- The membrane of the egg and sperm fuse and the sperm nucleus enters the egg
- Now fertilised, the nucleus of the secondary oocyte completes
meiosis II and then the egg and sperm nuclei fuse to form a diploid zygote
- The cortical granules
release enzymes that destroy the sperm-binding proteins on the jelly coat
And that's the end! Well done!
References
- https://ib.bioninja.com.au/higher-level/topic-11-animal-physiology/114-sexual-reproduction/animal-fertilization.html
- https://www.google.com/url?sa=i&url=http%3A%2F%2Fib.bioninja.com.au%2Fhigher-level%2Ftopic-11-animal-physiology%2F114-sexual-reproduction%2Freproductive-tissue.html&psig=AOvVaw15_OynqYQyMQsqT1vRDqZN&ust=1625304076168000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCPidwdOHxPECFQAAAAAdAAAAABAD
- https://www.google.com/url?sa=i&url=https%3A%2F%2Fstock.adobe.com%2Fimages%2Fthe-different-stages-of-oogenesis-diagram%2F275650696&psig=AOvVaw3g4LzYXFpzdJN24BjFPwJl&ust=1625304179110000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCNia74aIxPECFQAAAAAdAAAAABAi
- https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.shutterstock.com%2Fsearch%2Ffertilisation%2Bsperm&psig=AOvVaw0kxjAHZ30UMRTvJspPZP6K&ust=1625304305822000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCKi2tMKIxPECFQAAAAAdAAAAABAa
Drafted by Venetia (Biology)