Is the Y Chromosome Disappearing?
by Dr Jerry BergmanUnder the headline The Y chromosome is disappearing – so what will happen to men?, two genetics professors, Dr. Griffin and Dr. Ellis write, “The Y chromosome may be a symbol of masculinity, but it is becoming increasingly clear that it is anything but strong and enduring.” One wonders what evidence they have for making this prediction. Actually, none. Then where do they get this idea?As most adults know, in most mammals two X chromosomes produce a female, and an X and Y produce a male. Thus, it is the presence of the Y chromosome that determines a male. Although the Y chromosome influences over 200 different traits, one area of this chromosome, specifically where the SRY genes are located, triggers the major traits that produce males. If the SRY genes transpose from the Y chromosome to the X chromosome, an XX female will develop into to a male. This condition is very rare, but it does happen occasionally.Without the Y chromosome there would be no males, and thus no reproduction, so why do some scientists conclude it is disappearing? The reason is the X and Y chromosomes are thought to have evolved from a pair of identical autosome chromosomes that diverged from 100s of millions ago. 300 million years ago is another estimate, and a newer estimate puts the number at closer to 166 million years ago. Given such wide guesstimates, it is obvious that no one has any idea when they diverged, assuming they did.Even the divergence theory itself is not based on evidence, but on assumptions that in turn are based on Darwinian assumptions. The theory goes like this: over eons of time, genes that were beneficial for males either evolved by the accumulation of mutations on their Y chromosome, or were acquired through translocation (the movement of genes from other chromosomes to the Y chromosome).X and Y. Credit: Science Photo LibraryThe question of how mammals reproduced before this is answered by looking at all life forms and realizing the most primitive, such as bacteria, reproduce asexually by cloning, and other, more advanced life forms, reproduce sexually. The relatively puny human Y now contains only 78 genes and the human X has a whopping 1,098 known genes. This means human females have over 1,000 more genes than males.Because the Y chromosome is a small fraction of the X, from the primate genome which it is believed to have evolved, it is assumed the human Y chromosome has lost 1,393 of its 1,438 original genes over the course of its existence. Linear extrapolation of this 1,393-gene loss over 300 million years produces a genetic loss rate of 4.6 genes per million years. Extrapolating this forward means, Professors Griffin and Ellis claim, in 4.6 million years the Y chromosome would lose all of its functions.It is the creationists that predict degeneration of the genome from Adam’s perfect mutation free genome to our modern human. Humans suffer from over 5,000 diseases caused by the accumulation of mutations in our gamete genome. Furthermore, the human Y chromosome is exposed to high mutation rates due to the fact that it is passed on exclusively through comparatively unprotected sperm, which undergo multiple cell divisions during gametogenesis. Each cell division increases the risk of mutations, and the more cell divisions, the more mutations that result. Additionally, sperm are stored in a highly oxidative (thus mutation prone) environment compared to the cells inside the body that are protected by several mechanisms. These two conditions put the Y chromosome at a greater mutation risk than the rest of the genome. All this supports the creation view, not the Darwinian view which teaches that evolution improves the species and evolves it to more advanced levels of evolution.Because the current estimate is that a 30 percent difference exists between humans and chimps, it is assumed that the Y chromosome was, and thus is, one of the fastest-evolving parts of the human genome. In the terminal stages of the Y chromosome degeneration, the story goes, other chromosomes will take over its genes and thus its functions. Thus, evolution will take us all the way back to the pre-Y chromosome stage of development that existed 100s of millions, 300 million or 160 million years ago! In the end, the Y chromosome they predict will disappear entirely, and a new sex-determining system will arise like the one that existed 100s of millions, 300 million or 160 million years ago. As is obvious, this is rampant speculation based on the varieties of reproduction existing in some animals.On the other side, comparisons of human and chimpanzee Y chromosomes indicate that the human Y chromosome has not lost any genes since the hypothetical human and chimpanzee divergence, estimated between 6 and 7 million years ago. One 2012 report claimed that only one gene had been lost since humans diverged from the rhesus macaque 25 million years ago.These facts provide direct evidence that the linear extrapolation model is seriously flawed, and the human Y chromosome is either no longer shrinking, or shrinking at a much slower rate than the 4.6 genes per million years estimated by the linear extrapolation model. In short, this topic, as is true of much of Darwin theory, involves massive speculation and illustrates the need to examine the data used to determine some conclusions in evolutionary tales. It also illustrates the problem the public has when it uncritically accepts a claim when scientists make authoritative sounding propositions supposedly based on a select few scientific facts.See also Dr Bergman’s earlier post on this subject, “The problem with males: Y chromosome degeneration” (1 Nov 2017). https://theconversation.com/the-y-chromosome-is-disappearing-so-what-will-happen-to-men-90125. Rice, W. R. 1996. Evolution of the Y sex chromosome in animals. Bioscience. 46, 331–343. Warren WC, Hillier LD, Graves JA, et al. (2008). “Genome analysis of the platypus reveals unique signatures of evolution”. Nature. 453 (7192): 175–183 Graves, Jenny. 2016. Evolution of vertebrate sex chromosomes and dosage compensation. Nature Reviews Genetics, 17 (1) 33-46. January. Kettlewell, Julianna. 2005. Female chromosome has X factor. Females are genetically more varied than males, an analysis of the X chromosome has revealed. http://news.bbc.co.uk/2/hi/science/nature/4355355.stm Graves, J. A. M. (2004). “The degenerate Y chromosome—can conversion save it?”. Reproduction Fertility and Development. 16 (5): 527–534 Graves, Jenny. 2004. “The degenerate Y chromosome—can conversion save it?”. Reproduction Fertility and Development. 16 (5): 527–534. Graves, Jenny. 2006. “Sex chromosome specialization and degeneration in mammals”. Cell. 124 (5): 901–914. Wade, Nicholas. 2010. “Male Chromosome May Evolve Fastest”. New York Times. January 13. Hughes, Jennifer F.; et al. 2005. “Conservation of Y-linked genes during human evolution revealed by comparative sequencing in chimpanzee.” Nature. 437 (7055): 100–103. Callaway, Ewen. 2012. The human Y chromosome is here to stay. The male sex-determining chromosome has lost only one gene in 25 million years. February 22. https://www.nature.com/news/the-human-y-chromosome-is-here-to-stay-1.10082. Hsu, Christine. “Biologists Debunk the ‘Rotting’ Y Chromosome Theory, Men Will Still Exist”. Medical Daily. http://www.medicaldaily.com/biologists-debunk-rotting-y-chromosome-theory-men-will-still-exist-239833 Hughes, Jennifer F.; et al. 2010. Chimpanzee and human Y chromosomes are remarkably divergent in structure and gene content. Nature. 463, 536-539. January, 28.Author Jerry Bergman, PhDDr Jerry Bergman, professor, author and speaker, is a frequent contributor to Creation-Evolution Headlines. He is currently a staff scientist at the Institute for Creation Research (ICR). See his Author Profile for his previous articles and more information.(Visited 1,547 times, 1 visits today)FacebookTwitterPinterestSave分享0