Gamets

Gamets, or gametes, are haploid reproductive cells that unite during sexual reproduction to form a zygote. They carry half the genetic complement of an organism and are produced by specialized tissues through a process called gametogenesis. The fusion of two gametes restores the diploid chromosome number in the offspring and introduces genetic variation through recombination and independent assortment.

Most animals produce two main types of gametes: males produce small, motile sperm cells; females produce larger, nutrient-rich egg cells. In plants and many algae, the terms pollen (male gametophyte) and ovule (female gametophyte) are used, with fertilization often occurring after pollen is transferred to the female reproductive structure.

Gametogenesis includes spermatogenesis and oogenesis in animals; in plants it occurs within the male and female gametophytes. The process ensures haploidy at the gamete stage; meiosis produces haploid cells with genetic variation due to crossing over during prophase I and random assortment of chromosomes.

Fertilization results when two gametes fuse, forming a zygote that develops into a new individual. The specific mechanisms and timing of fertilization vary widely: internal fertilization in many animals, external fertilization in many aquatic species, and pollen grain germination triggering fertilization in flowering plants.

Some species exhibit isogamy, where gametes are morphologically similar, while others exhibit anisogamy, with distinct gamete types. In many life cycles there is an alternation of generations, with a diploid sporophyte producing spores that grow into haploid gametophytes that generate gametes again.