Reproduction in Animals

Sexual Reproduction

How do you think generations continue on earth? How do dogs give birth to puppies? More importantly, how did you get your life? Yes! This is the process of reproduction. In this chapter, we will study more about sexual reproduction. This is the process that we human beings follow. Before we get into the details, we will first look at what reproduction is all about!

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What is Reproduction?

Reproduction is a life process which enables an organism to reproduce its own offspring. Thus, they continue their species without extinction. Reproduction can take place by the participation of a single parent or two parents.  Based on this, we can classify reproduction into two types.

  • Asexual reproduction: A type of reproduction where a single parent is divided by itself and reproduce its offspring.
  • Sexual reproduction: A process where two parents participate in producing their offspring.

Let us study about sexual reproduction in this chapter. We will talk about asexual reproduction in another chapter.


Sexual Reproduction

Sexual reproduction is a natural way of reproduction in humans, animals and the majority of plants also choose to reproduce sexually. This type of reproduction is more complex and lengthy as compared to asexual reproduction. Moreover, reproducing sexually gives the benefit of variation and offsprings are unique. Sexual reproduction consists of a set of events. We can divide it into three stages: Pre-fertilization, Fertilization, and Post-fertilization.

Browse more Topics under Reproduction In Animals

Learn about Asexual Reproduction in more detail here.

The Stages of Sexual Reproduction

Below, we will discuss the various stages of sexual reproduction.

1) Pre-fertilization

This stage involves the events prior to fertilization. Gamete formation (gametogenesis) and transfer of gamete are the two processes that take place during this stage. Gametes are sex cells which are haploid (23 chromosomes) in nature and are distinct in males and females.

Male gamete is called sperm whereas female gamete is called ovum or egg. In every organism, these gametes form within special structures. Since female gamete is immobile, male gametes need to be transferred for fertilization. In plants, this is pre-fertilization happens through pollination. Unisexual animals transfer gametes by sexual intercourse.

2) Fertilization

The process in which the haploid male and female gametes meet and fuse together to form a zygote is fertilization or syngamy. This can occur either outside the body known as External fertilization or inside the body known as Internal fertilization.


(Source: Slideshare)

3) Post-fertilization

Fertilization results in diploid zygote formation. Eventually, the zygote divides mitotically and develops into an embryo. This process is called embryogenesis. During embryogenesis, cells differentiate and modify accordingly. Zygote development depends on the organism and its life cycle.

Animals are classified into oviparous and viviparous based on whether the zygote develops outside or inside the body respectively. In angiosperms, zygote develops into the ovary and ovary transforms into fruit while ovules develop into seeds.

Here’s a Solved Question for You

Q: Write a note on types of fertilisation in animals.

Ans: There are two types of fertilization in animals, viz. external fertilization and internal fertilization.

  • External Fertilisation: When fertilization takes place outside the animal’s body, it is external fertilization. Most of the aquatic animals show external fertilization, e.g. fish and frog. A large number of eggs need to be fertilized in this method because most of the fertilized eggs get washed away by water or are eaten by predators. A large number of eggs ensures the survival of some of the offspring.
  • Internal Fertilisation: When fertilization takes place inside the animal’s body, it is internal fertilization. Internal fertilization happens in most of the terrestrial animals. Unlike external fertilization, there is no need to produce a large number of eggs in internal fertilization.
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