Also referred to as sex cells, gametes are reproductive cells of an entity. These are haploid cells wherein each of it carries one copy of chromosome. Male gametes are known as sperms while female gametes are known as ova or eggs. The reproductive cells are an outcome of the process of meiosis.
During this type of cell division, the diploid parent cell having two copies of each chromosome experiences one round of DNA replication followed by two distinct cycles of nuclear division to generate four diploid cells. In turn, these cells go on to form the ova or the sperm.
Sperms are developed in the testes of males while the ova matures in the ovaries of females. Each of the spermatozoan or the sperm cell is motile and small. It has a flagellum enabling the cell to move and propel. The ovum or the egg cell on the other side is comparatively large and non-motile. During fertilization, these haploid cells fuse forming diploid entities.
Ova and sperms are the most common gametes. These differ in size and are haploid in nature. They may experience external or internal fertilization. There are some entities, however, that produce both of these cells in the same entities. Such organisms are known as hermaphrodites. Majority of entities who reproduce sexually produce one type of gamete.
Formation of Gametes
Meiosis, a two-step process gives rise to gametes. The outcome of this process is 4 haploid daughter cells, each of which contains only one set of chromosomes. Through the process of fertilization (which can either be external or internal), they unite forming the zygote. The zygote is the future foetus which is diploid in nature containing two sets of chromosomes, each from both the parents.
Modes of Sexual Reproduction
The shape and size of gametes largely decide the mode of sexual reproduction. While some male and female gametes are almost of the same size, some others vary by a large margin. In a few species of fungi and algae, both male and female gametes are almost of the same size and are motile. When two similar gametes unite, it is isogamy. While the formation of gametes having dissimilar shapes and sizes is known as heterogamy or anisogamy. There is a particular form of anisogamy called oogamy observed in higher species of animals and plants (also in some fungi and algae). In this, the female gamete is much larger and is non-motile compared to its male counterpart. This is the reproduction observed in humans.
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