Reproduction is the process through which organisms produce their offspring. It is a crucial process as it allows organisms to continue their species and prevents them from going extinct altogether.
In a broad sense, reproduction is divided into two types – sexual and asexual. In this article, we will discuss sexual reproduction and its different stages.
With that being said, let’s proceed to find out more about what is sexual reproduction.
What is Sexual Reproduction?
The process of sexual reproduction is a method in which genetically diverse offspring come into existence. It occurs when genetic information of two individuals of different sex is combined.
When compared to the other type of reproduction, sexual reproduction is more complicated as a process.
Here are the different types of sexual reproduction –
Allogamy
Internal fertilisation
External fertilisation
Autogamy
Two types of sexual reproduction which are common in human beings and animals are internal fertilization and allogamy, respectively.
Test Your Knowledge: What is sexual reproduction? Define the role of chromosomes in sexual reproduction.
Stages of Sexual Reproduction in humans
Typically there are three stages of reproduction in humans, namely – pre-fertilization, fertilization, fertilization and post-fertilization.
Let’s check them in detail -
Pre-fertilization
Gametogenesis - the formation of gametes and transfer of gametes are two of the main events of pre-fertilization stage. In gametogenesis, two types of gametes i.e. male and female haploid cells, are formed.
These morphologically distinct gametes are known as heterogametes. The male gamete is called sperm or antherozoid, and ovum or egg is the female gamete.
In case of some algae, these gametes are often quite similar. This, however, makes it challenging to categorise them as male and female. Usually, these gametes are called homogametes or isogametes.
The fact female gamete is immovable makes it essential to transfer male gametes to initiate the process of fertilization.
In unisexual animals, gametes are transferred through sexual intercourse whereas, in case of plants, the said transfer is facilitated through pollination.
DIY: Find out about cell division in the context of gamete formation. Explain what happens to haploid during cell division.
Fertilization
Arguably, fertilization is one of the most significant events in sexual reproduction and is also known as syngamy. It is a process wherein male and female gametes fuse to form a diploid zygote.
Typically, fertilization tends to occur either inside (internal fertilization) or outside the body of an organism (external fertilization).
Notably, in certain organisms like honeybees, rotifers, turkey and some lizards, the female gametes can form a new organism without being fertilized. Such a phenomenon is known as parthenogenesis.
Post-fertilization
It is the last of the sexual reproduction steps. The main highlights of this said stage are – embryogenesis and cell division.
In simple words, embryogenesis is the process in which a zygote develops into an embryo. It is during embryogenesis that the zygote goes through both cell division and cell differentiation.
Additionally, they are responsible for the modification and formation of tissues and organs and facilitate the formation of an organism.
Based on the site of zygote’s development, animals are - viviparous and oviparous. Also, in flowering plants, the ovary starts developing after fertilization. Subsequently, the ovules mature, which contain the embryo.
True or False: In viviparous animals, the zygote develops inside the female organism’s body.
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FAQs on An Overview of Sexual Reproduction
1. List six specific characteristics of sexual reproduction.
Characteristics are - i) The process requires two individuals (male and female). ii) Gametes are formed through reductional division. iii) Fertilization is the process of fusion of gametes iv) Fertilization facilitates zygote formation. v) Sexual reproduction is responsible for variation in offspring vi) Maintains chromosome number in species.
2. Which process leads to the formation of gametes?
Gametogenesis is the process of formation of gametes, wherein two distinct sex cells, i.e. male and female haploids, are formed. The entire process takes place in the pre-fertilization stage of sexual reproduction.
3. What is the function of sexual reproduction?
These are the functions of sexual reproduction in plants, animals and human beings – a) creates new organisms, b) is responsible for variation in progeny c) prevents a species from going extinct.
