gametogenesis

Gametogenesis is the process by which haploid gametes are produced from diploid germ cells. It includes the meiotic divisions and related cellular changes that prepare reproductive cells for fertilization. In most animals, gametogenesis occurs in the gonads—testes in males and ovaries in females—while in plants and fungi similar processes generate the reproductive cells that participate in fertilization.

In animals, male gametogenesis is called spermatogenesis. It starts with spermatogonia in the seminiferous tubules, which divide by mitosis and enter meiosis to form primary spermatocytes. Meiosis I yields two haploid secondary spermatocytes, and meiosis II produces four haploid spermatids. Spermiogenesis then transforms these into mature spermatozoa, which are released and mature in the epididymis.

Female gametogenesis is called oogenesis. In mammals, it begins before birth when oogonia become primary oocytes paused in prophase I. At puberty, selected primary oocytes resume meiosis; meiosis I yields a secondary oocyte and a first polar body. Meiosis II is usually completed after fertilization, yielding a haploid ovum and a second polar body. Cytoplasmic partitioning supports early embryonic development.

In plants and many fungi, similar processes generate male and female gametophytes or gametes. In flowering plants, microsporogenesis and megasporogenesis produce microspores and megaspores, which develop into pollen grains (male gametophytes) and embryo sacs (female gametophytes). Fertilization then combines genetic material from two gametes to form a diploid zygote.

Regulation of gametogenesis involves hormones such as FSH and LH in animals, and local signaling in other groups. Failures in meiotic division or chromosome segregation can cause infertility or aneuploidy. Studying gametogenesis is essential to reproductive biology, agriculture, and assisted reproduction.