 |
| What is Sexual Reproduction? |
Here I have discussed the overall concept of Sexual Reproduction. Basically I am going to explain the topic Sexual Reproduction from the chapter “Reproduction in Organisms” of Biology NCERT textbook.
Introduction
A special type of reproduction where male & female gamete are formed by either same indivisual or different indivisual of opposite sex and give progeny by the fusion of those gamets.
The process is slow, complex & elaborate as compered to Asexual Reproduction.
Though the sexually reproducing organisms differ so greatly in Morphology, Anatomy & Physiology, they share a similer pattern in terms of Sexual Reproduction.
 |
| Sexual Reproduction characteristic features |
Events in Sexual Reproduction
As I have mentioned earlier sexual reproduction is an elaborate processes, it is complete by some events which follow a regular sequence.
Sexual reproduction is characterized by formation of male & female gametes, fusion of that gametes followed by formation of zygote and embryo.
The most vital step of sexual reproduction is fusion of gametes i.e, Fertilisation.
So making a reference to the fertilisation, the whole process is grouped into three distinct stages—
1. Pre-fertilisation
2. Fertilisation
3. Post-fertilsation
Pre-fertilisation events
All the phenomena just before the fusion of gametes include under Pre-fertilisation events.
The two main pre-fertilisation events are gametogenesis & gamete transfer.
Gametogenesis
The term gametogenesis is a combination of two words, ‘gamete‘ & ‘genesis‘.
In biology, ‘genesis’ term is used to mean ‘formation’. So gametogenesis means formation of gamete.
 |
| Gametogenesis |
But majority of sexually reproducing organisms produced Heterogametes, morphologically different type of male & female gametes.
Gamete Transfer
As the male & female gametes are produced at different body or different part of body, they should to transfer for fusion.
 |
| Motility of Gamete |
In a majority of organisms including humans, male gamet is motile while female gamet is non-motile.
But there have two exceptional case.
In fungi & algae (exepct – Rhodophyceae), male & female both type of gametes are motile.
In gymnosperm, angiosperm & red algae, male & female both type of gametes are non-motile.
Fertilisation
A process by which male & female gamete are fused to form zygote. It also termrd as Syngamy.
The fusion of gamete may occour either inside the body or in the external medium, i.e, outsite the body.
If fertilisation occour inside the body then the process is called Internal fertilisation. Fungi, plants like Bryophytes, Pteridophytes, Gymnosperm & Angiosperm and higher animals such as Reptiles, Birds, Mammals exhibit internal fertilisation.
In many Algae, Fishes and Amphibians syngamy occours in water (external medium) which is called External fertilisation.
Post-Fertilisation Events
After the gametic fusion to embryo formation is referred as Post-fertilsation events.
The Zygote
The result of syngamy is named as Zygote. Formation of the diploid zygote is universal in all sexually reproducing organisms. Every sexually reproducing organism begin life as a single cell zygote. Zygote ensures continuity of species generation after generation.
 |
| Embryogenesis |
Embryogenesis
The process of development of embryo from zygote is called Embryogenesis.
Under this process zygote devide by mitosis and form a multicelluler embryo.
Along with division, the cells undergo differentiation which helps to make certain modifications to form specialised tissue and organs to form an organisms.
Conclusion
This is the whole events of sexual reproduction. As the offspring is produced by fusion of two gamete from opposite sex, they are neither identical to their parent nor themselves. That’s why Sexual Reproduction create variations from generation to generation which is important for evolution.