The reproductive cells of a living creature are called gametes, also known as sex cells. Male and female gametes are referred to as ova or egg cells, respectively. Gametes are the reproductive cells of an organism, which are haploid cells with only one copy of each chromosome. Meiosis is a type of cell division that results in the formation of reproductive cells.

During meiosis, a diploid parent cell with two copies of each chromosome undergoes one round of DNA replication followed by two rounds of nuclear division, yielding four haploid cells. These cells develop into sperm or ova. Female ova mature in the ovaries, while male sperm grow in the testes. Each sperm cell, a spermatozoon, is a tiny, mobile cell. A spermatozoon and an ovum combine to generate a new diploid organism during fertilisation.

Development of Gametes

Isogamy is widely considered as the original state, out of which the anisogamy or heterogamy emerged, despite the fact that there are no historical traces of its evolution. Isogamy gave way to anisogamy, which led to oogamy.

All analyses reveal that intermediate gamete sizes are removed due to selection; hence, there are virtually always just two gamete kinds. Intermediate-sized gametes do not have similar advantages as tiny or large gametes; in terms of mobility and quantity, they are inferior to small gametes, and in terms of supply, they are inferior to large gametes.

Heterogametes

Heterogamy is a term that refers to a wide range of phenomena in various scientific fields. “Hetero” usually refers to a difference, while “gamy” refers to reproduction.

In reproductive biology, heterogamy refers to the alternation of generations, such as parthenogenetic and sexual generations. Some aphids, for example, exhibit heterogamy.

Alternatively, heterogamy or heterogamous is sometimes used as a synonym for heterogametic, which refers to the presence of two chromosomes that are not identical in sex. The heterogamous sex, for example, consists of XY males and ZW females.

The sex of a species in which the sex chromosomes are not identical is known as heterogametic sex. Males with an X and a Y chromosome are known as the heterogametic sex, whereas females with two X chromosomes are known as the homogametic sex. The XY sex-determination system refers to this configuration.

On the other hand, males in birds and certain reptiles have two Z chromosomes and are homogametic, whereas females have one Z and one W chromosome and are heterogametic. Lepidopterans (butterflies and moths) have heterogametic females; however, males are the heterogametic sex in Drosophila. This arrangement is identified as the ZW sex-determination structure.

Heterogamesis can result in a lack of or limited meiotic recombination between the sex chromosomes, and in some species, this can even extend to the autosomes, a condition known as achiasmy. Male Drosophila melanogaster flies, for example, are predominantly achiasmatic, with no recombination on all chromosomes, whereas females exhibit recombination.

Sexual Reproduction in Plants

Plants that reproduce sexually create gametes as well. However, because plants have a life cycle that alternates between diploid and haploid generations, there are certain variations. Meiosis is used by plants to produce spores, which mature into multicellular haploid gametophytes, which then produce gametes by mitosis. The sperm are produced in the antheridium, whereas the egg cells are produced in the archegonium, a flask-shaped organ.

In flowering plants, the female gametophyte is generated inside the ovule within the ovary of the flower. When the haploid gametophyte reaches maturity, it produces female gametes that are ready for fertilisation. A pollen grain within the anther produces the male gametophyte. When pollen grains settle on a mature stigma of a flower, they germinate and create a pollen tube, which grows down the style into the flower’s ovary, and then into the ovule. By mitosis, the pollen produces sperm, which is subsequently released for fertilisation.

Difference between Heterogametes and Homogametes

Heterogametes	Homogametes
The two gametes have different morphologies.	The two gametes have identical morphologies, also known as isogametes.
These gametes are produced in sexually competent organisms.	These gametes are produced by Algae and fungi.
Gymnosperms and angiosperms are two common examples.	Rhizopus and Ulothrix are two common examples.

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Frequently Asked Questions (FAQs)

Define heterogametes. What do we call these gametes individually?

Hetergametes are two physically different gametes produced mostly by sexually reproducing organisms.
Antherozoid or sperm refers to the male gamete, while egg or ovum refers to the female gamete.

Why is syngamy a major event in sexual reproduction?

Syngamy, or fertilisation, is the union of a male gamete with a female gamete, and it plays a vital part in the genetic exchange that leads to the production of a diploid zygote.

What regulates the reproduction processes and the associated behavioural expressions in organisms?

Hormones and some environmental factors interact to regulate organisms’ reproductive processes and accompanying behavioural responses.

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