Gametes Definition, Types, Formation in Plants and Animals

Gametes Meaning: Gametes are specialized cells involved in sexual reproduction. They fuse during fertilisation to form a zygote, the initial cell of a new organism. In sexual reproduction, male gametes, known as sperm, and female gametes, known as ova or eggs, are essential. Sperm are motile cells equipped with a flagellum to move towards the egg. In contrast, ova are non-motile and relatively larger compared to sperm.

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Gametes Definition

Mammary Glands

Gametes Types

1. Isogamy: In this type of gamete fusion, the gametes are similar in morphology, meaning they have the same size and shape. This condition is also known as "heterogamy." Isogamous gametes are not classified as male or female but are represented as "+" or "-." Examples include the gametes of unicellular algae such as Chlamydomonas reinhardtii and Carteria palmata.
2. Anisogamy: This involves gametes with different morphologies, specifically in size and shape. Anisogamous gametes are classified as male and female, with the smaller gamete being the sperm or male gamete, and the larger gamete being the ova, egg, or female gamete. Anisogamous gametes can be motile or non-motile.
3. Oogamy: In this type, one gamete (sperm) is motile, while the other (egg) is non-motile. This is the case in humans and mammals, where a motile sperm fertilise a non-motile egg to form a zygote.
4. Microgametes and Macrogametes: Gametes can also be classified based on size. Microgametes are smaller, motile gametes produced in large numbers without nutrient storage, such as sperm cells. Macrogametes, on the other hand, are larger, non-motile gametes produced in limited numbers with a significant nutrient store, like egg cells or ova.

Okazaki Fragments

Gametes Formation

1. Replication: During meiosis I, a diploid germ cell replicates its DNA, resulting in each chromosome having two sister chromatids.
2. Pairing and Crossing Over: Homologous chromosomes (chromosomes that code for the same traits) pair up and exchange sections of their DNA in crossing over. This genetic exchange increases genetic diversity in offspring.
3. Separation of Homologous Chromosomes: Homologous chromosomes then separate and move to opposite ends of the dividing cell.
4. Meiosis II: In this step, the sister chromatids are separated and move to opposite sides of the dividing cell, resulting in four haploid daughter cells.

lymphocytes

Gametes in Plants

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Gametes in Animals

• Sperm, the male gametes, are small, mobile cells containing half of the organism's genetic information (DNA). They are produced in the testes of male animals.
• Ova (or eggs), the female gametes, are significantly larger than sperm and contain the other half of the organism's DNA. They are produced in the ovaries of female animals.

1. Gametes are haploid, meaning they contain only one set of chromosomes.
2. Gametes are produced through a cell division process called meiosis, which reduces the number of chromosomes in a cell by half.
3. Sperm and ova differ greatly in size and mobility. Sperm are small and able to move, whereas ova are large and stationary.
4. Fertilisation is the process by which a sperm cell combines with an egg cell to form a zygote.

Gametes are Haploid or Diploid

Gametes Example