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An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell (PGC), which then undergoes mitosis, forming oogonia. During oogenesis, the oogonia become primary oocytes. An oocyte is a form of genetic material that can be collected for cryoconservation.
In many algae (e.g., Chara), the main plant is haploid; oogonia and antheridia form and produce haploid gametes. The only diploid part of the life cycle is the spore (fertilized egg cell), which undergoes meiosis to form haploid cells that develop into new plants. This is a haplontic life cycle (with zygotic meiosis).
The primary oocyte is defined by its process of ootidogenesis, which is meiosis. [2] It has duplicated its DNA, so that each chromosome has two chromatids, i.e. 92 chromatids all in all (4C). When meiosis I is completed, one secondary oocyte and one polar body is created. Primary oocytes have been created in late fetal life.
The diploid zygote undergoes repeated cellular division by mitosis to grow into the organism. In the haplontic life cycle (with post-zygotic meiosis), the organism is haploid, by the proliferation and differentiation of a single haploid cell called the gamete. Two organisms of opposing sex contribute their haploid gametes to form a diploid zygote.
In fact, a primary oocyte is, by its biological definition, a cell whose primary function is to divide by the process of meiosis. [16] However, although this process begins at prenatal age, it stops at prophase I. In late fetal life, all oocytes, still primary oocytes, have halted at this stage of development, called the dictyate.
Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes.Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitosis.
Oocyte maturation is the following phase of oocyte development. It occurs at sexual maturity when hormones stimulate the oocyte to complete meiotic division I. The meiotic division I produces 2 cells differing in size: a small polar body and a large secondary oocyte.
Oogenesis, the process of female gamete formation in animals, involves meiosis (including meiotic recombination) of a diploid primary oocyte to produce a haploid ovum. Spermatogenesis, the process of male gamete formation in animals, involves meiosis in a diploid primary spermatocyte to produce haploid spermatozoa. In animals, ova are produced ...