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- Feb 12, 2017
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I have noticed that, in another thread, some posters were trying to justify the atrocious misnomer of "fertilized egg", referring to a zygote, by claiming that, while the entire egg cell remains and contributes to the zygote, not all of the sperm cell fertilizes the egg, during the process of fertilization. This is just flat-out untrue. First of all, the entire sperm enters the egg during fertilization, including even the midpiece of the sperm, which contains the mitochondria of the sperm. That's right, zygotes and early embryos have paternal mitochondria, although they are later removed via a substance called ubiquitin, explaining why they are usually not present after birth (although there are rare cases of adults who have retained paternal mitochondria). (SOURCE: http://m.pnas.org/content/93/24/13859.full.pdf).
Also, a user has claimed on some thread that the sperm only contributes half of the contents of the nucleus of the zygote, whereas the egg contributes everything else. This is utterly and patently untrue. First of all, the paternal pronucleus (the nucleus from the sperm) actually tends to be a bit larger than the maternal pronucleus (the nucleus from the egg) in most zygotes. Second of all, the sperm contributes more than just its nucleus to the zygote. It contributes its plasma membrane, which fuses to that of the egg, its cytoplasm, containing many RNA's, and, most crucially, a very important cell organelle called the centrosome, containing two structures called centrioles, which, in most species (with the exception of rats and mice) is contributed only by the father, as egg cells do not have them. The centrosome creates the cytoskeleton of the cell, mainly microtubules, although it has also been shown that it appears to create the other two types of cytoskeletal proteins, actin filaments and intermediate filaments, as well. The microtubules synthesized, or nucleated, by the centrosome form a structure called the mitotic spindle, which segregates chromosomes on either pole of the cell in preparation for cell division during the process of mitosis.
In fact, in the zygote, the microtubules formed from the paternal centrosome emanate outwards from it, and pull the maternal pronucleus and the paternal pronucleus together, causing them to merge, in a process known as syngamy, causing the zygote's genetic material to be enclosed within one nuclear compartment, rather than two.
Furthermore, studies seem to show that paternal RNA's and chemicals transmitted from the sperm to the zygote can transmit epigenetic paternal phenotypes to the offspring, furnishing indisputable proof of what is already known to anyone who has done the faintest job of acquainting themselves with the biology of fertilization: that the sperm obviously contributes much more than just its nucleus to the zygote.
Also, a user has claimed on some thread that the sperm only contributes half of the contents of the nucleus of the zygote, whereas the egg contributes everything else. This is utterly and patently untrue. First of all, the paternal pronucleus (the nucleus from the sperm) actually tends to be a bit larger than the maternal pronucleus (the nucleus from the egg) in most zygotes. Second of all, the sperm contributes more than just its nucleus to the zygote. It contributes its plasma membrane, which fuses to that of the egg, its cytoplasm, containing many RNA's, and, most crucially, a very important cell organelle called the centrosome, containing two structures called centrioles, which, in most species (with the exception of rats and mice) is contributed only by the father, as egg cells do not have them. The centrosome creates the cytoskeleton of the cell, mainly microtubules, although it has also been shown that it appears to create the other two types of cytoskeletal proteins, actin filaments and intermediate filaments, as well. The microtubules synthesized, or nucleated, by the centrosome form a structure called the mitotic spindle, which segregates chromosomes on either pole of the cell in preparation for cell division during the process of mitosis.
In fact, in the zygote, the microtubules formed from the paternal centrosome emanate outwards from it, and pull the maternal pronucleus and the paternal pronucleus together, causing them to merge, in a process known as syngamy, causing the zygote's genetic material to be enclosed within one nuclear compartment, rather than two.
Furthermore, studies seem to show that paternal RNA's and chemicals transmitted from the sperm to the zygote can transmit epigenetic paternal phenotypes to the offspring, furnishing indisputable proof of what is already known to anyone who has done the faintest job of acquainting themselves with the biology of fertilization: that the sperm obviously contributes much more than just its nucleus to the zygote.
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