Gametogenesis and Fertilization, The Two Processes That Continue Human Life
Gametogenesis And Fertilization requires proper gametogenesis (oogenesis in the female and spermatogenesis in the male), which produces haploid cells and introduces diversity. Read the article to know more.
Dr. Nivedita7 Aug, 2024
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Gametogenesis is the process of making gametes in both male and female sexes. Gametes are haploid cells (with half the set of chromosomes found in a normal
human cell) which, when fused, lead to the formation of a zygote. A zygote is the first cell of a diploid organism (with the same set of chromosomes found in a normal human cell). Gametes are indispensable for sexual reproduction. Sexual reproduction is crucial for the survival of the human race as it introduces variations in the genetic code, which are selected by evolutionary forces, resulting in the selection of the fittest progeny. Thus, it ensures that only the best genetic code is transferred to future generations.Gametogenesis
In males, spermatogenesis, and in females, oogenesis is the process of gametogenesis. There are striking differences between the two. Spermatogenesis starts at puberty in males, whereas in females, it starts during embryonic development. The end goal of spermatogenesis is to create a large number of sperm, while in oogenesis, the end goal is to create a single ovum. The common theme between the two is that both involve a reductive division in which the number of chromosomes is halved from the original number in diploid organisms. This is followed by a multiplication division, leading to the production of a large number of haploid gametes. Thus, reductive division (meiosis) is the hallmark of gametogenesis.Spermatogenesis and Oogenesis
Spermatogenesis occurs in the testes and involves the transformation of spermatogonial stem cells into mature spermatozoa through several stages, including mitosis, meiosis, and spermiogenesis. This process is continuous and results in the production of millions of sperm each day. Oogenesis, on the other hand, occurs in the ovaries and is a more discontinuous process. It begins before a female is born, with primary oocytes arrested in prophase I of meiosis until puberty. Each menstrual cycle, typically one oocyte completes meiosis I and begins meiosis II, but it is only upon fertilization that meiosis II is completed. The result is a single mature ovum and polar bodies that are not functional gametes. This asymmetric division ensures that the ovum retains most of the cytoplasm and organelles necessary for early embryonic development.Fertilization
In fertilization, both male and female gametes fuse to form a zygote. The fusion of gametes is tightly regulated so that gametes of a single species can only fertilize each other. They have proteins on their surfaces, and many reactions occur on the surface of the gametes to ensure that one ovum is fertilized by only one sperm. The sperm must penetrate the outer layers of the egg, including the corona radiata and the zona pellucida. This penetration is facilitated by enzymes released from the sperm’s acrosome. Once a sperm successfully penetrates the egg, changes in the egg’s membrane prevent other sperm from entering, ensuring that the zygote remains diploid. The genetic material from the sperm and egg then combines, resulting in a zygote with a complete set of chromosomes. This zygote undergoes rapid cell division and begins the process of embryonic development. Both gametogenesis and fertilization are marvels of nature that are indispensable for the survival of the human race. They ensure genetic diversity and the continuation of life through successive generations.Gametogenesis and Fertilization FAQs
What are fertilizin and antifertilizin proteins?
Fertilizin is a glycoprotein released by the ovum that reacts with the antifertilizin of sperm. When sperm meet the ovum in the oviduct, they release antifertilizin. The sperm adheres to the surface of the egg due to the presence of fertilizin molecules on the surface of the egg cytoplasm.
What is infertility in a human male?
When less than 40 percent of human sperm do not have vigorous motility, the male is considered infertile. Sterility can also occur in human males due to complications from infections like mumps.
Why does asexual reproduction not occur in higher animals?
In asexual reproduction, all progeny are genetically identical, so evolutionary forces do not have anything to select for the most fit progeny. This means that the entire population could be eradicated in the event of hostile conditions. In higher animals, selection is essential for survival.
What is infertility in human females?
In females, there are myriad causes of infertility, but those related to gametogenesis include the premature depletion of follicles and failure to ovulate.
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