Gametes

Beginning of Life
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What Are Gametes?

Definition: Gametes are reproductive cells (sex cells) that unite during sexual reproduction to form a new cell called a zygote. Male gametes are sperm and female gametes are ova (eggs). In seed bearing plants, pollen is the male sperm producing gametophyte. Female gametes (ovules) are contained within the plant ovary. In animals, gametes are produced in male and female gonads. Sperm are motile and have a long, tail-like projection called a flagellum.

Ova however, are non-motile and relatively large in comparison to the male gamete.

Gamete Formation

Gametes are formed by a type of cell division called meiosis. This two step division process produces four daughter cells that are haploid. Haploid cells contain only one set of chromosomes. When the haploid male and female gametes unite in a process called fertilization, they form what is called a zygote. The zygote is diploid and contains two sets of chromosomes.

Gamete Types

Some male and female gametes are of similar size and shape, while others are different in size and shape. In some species of algae and fungi, male and female sex cells are almost identical and both are usually motile. The union of these types of gametes is known as isogamy. In some organisms, gametes are of dissimilar size and shape. This is known as anisogamy or heterogamy (hetero-, -gamy). Higher plants, animals, as well as some species of algae and fungi exhibit a special type of anisogamy called oogamy.

In oogamy, the female gamete is non-motile and much larger than the male gamete.