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Oogenesis occurs within the embryo sac and leads to the formation of a single egg cell per ovule. In ascaris, the oocyte does not even begin meiosis until the sperm touches it, in contrast to mammals, where meiosis is completed in the estrus cycle. In female Drosophila flies, genetic recombination occurs during meiosis.
Gametogenesis, the development of diploid germ cells into either haploid eggs or sperm (respectively oogenesis and spermatogenesis) is different for each species but the general stages are similar. Oogenesis and spermatogenesis have many features in common, they both involve: Meiosis; Extensive morphological differentiation
The process of spermatogenesis as the cells progress from primary spermatocytes, to secondary spermatocytes, to spermatids, to Sperm Cycle of the seminiferous epithelium of the testis. Spermatocytogenesis is the male form of gametocytogenesis and results in the formation of spermatocytes possessing half the normal complement of genetic material.
The sperm's tail and mitochondria degenerate with the formation of the male pronucleus. This is why all mitochondria in humans are of maternal origin. Still, a considerable amount of RNA from the sperm is delivered to the resulting embryo and likely influences embryo development and the phenotype of the offspring. [23]
In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts or other "over-wintering" stages of sexual reproduction ensure the survival during unfavorable times and the organism can "wait out ...
The formation of an oocyte is called oocytogenesis, which is a part of oogenesis. [1] Oogenesis results in the formation of both primary oocytes during fetal period, and of secondary oocytes after it as part of ovulation.
Only 1 in 14 million of the ejaculated sperm will reach the fallopian tube. The egg simultaneously moves through the fallopian tube away from the ovary. One of the sperm encounters, penetrates and fertilizes the ovum, creating a zygote. Upon fertilization and implantation, gestation of the fetus then occurs within the uterus. [11] [12] [13] [14]
Because its main function is to nourish developing sperm cells through the stages of spermatogenesis, the Sertoli cell has also been called the "mother" or "nurse" cell. [10] Sertoli cells also act as phagocytes, consuming the residual cytoplasm during spermatogenesis. Translocation of cells from the basal lamina to the lumen of the ...