X chromosome in mice and men reported in The Scientist, ScienceNOW and ScienceDaily. David Page, a geneticist at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, and colleagues have carried out a detailed study of the X chromosome in order to fill in gaps left when the chromosome was first sequenced over a decade ago. The X chromosome is considered to be the female chromosome, although it has long been known to carry genes for general body functions needed by both males and females. They found that many genes on the chromosome existed as single copies, but there were also regions containing long palindromic sequences, i.e. mirror image copies of genes. These regions are called ampliconic regions.
Page’s team also wanted to test “Ohno’s law”, an idea proposed in the 1960’s by Susumu Ohno, which, according to the researchers, “states that the gene content of X chromosomes is conserved across placental mammals”. This means it has not evolved as much as other chromosomes, and therefore human X chromosome should be very similar to that of mammals, such as mice. The research team compared the results of their detailed sequence of the human X with the mouse X. The X chromosome contains approximately 800 genes and the researchers found some 340 genes that were not shared between mice and men. According to ScienceNOW: “There are 144 human X chromosome genes with no counterparts in mice, and 197 such mice genes are unique. Of the 144 human ones, 107 exist in multiple copies in the newly sequenced duplicated regions of the X and seem to be changing rapidly. Based on such evidence, Page concludes that these genes have appeared since the ancestors of mice and humans split off from each other”. Jianzhi Zhang, an evolutionary geneticist at the University of Michigan, Ann Arbor, commented: “I am surprised by the large number of unshared genes between the human X and mouse X. The finding suggests that X chromosome gene content is probably changing all the time”.
The other interesting thing about the genes in the ampliconic regions is that some of them are expressed in distinctly male tissues, and are not expressed at all in females, and some even seem to have a role in sperm production.
Editorial Comment: The fact that the X chromosome has some genes needed in male tissues is not all that surprising when you consider the Biblical origins of man and woman. The X chromosome is currently regarded as the female chromosome because females have two X’s, and they need both to develop female reproductive organs and to be fertile. Males have one X chromosome, but also need a male determining Y chromosome. Therefore, Adam was created with one X and one Y, and needed both to function normally. Since God made Adam first and equipped him with both X and Y chromosomes needed to exhibit maleness, then followed up by making the woman from Adam’s tissue, He had all necessary components needed to make a human female. He just had to give Eve a duplicate X, instead of the Y. Thus, Eve with two copies of the X was a unique creation, but still one flesh with Adam. It is therefore not so strange that the supposed female X chromosome carries genes needed for male function, because from Adam’s time onwards males would inherit their one X chromosome only via their mothers.
The discovery of genes that are not shared between mice and men does not prove any genes have changed. It simply prove they are different, and it is consistent with the Biblical teaching that mice and men were never related, but were separate created kinds, each with an appropriate X chromosome genes built by the Creator. Perhaps Ohno’s Evolution law should be revised to “Evolution – Oh no!” (Ref. genetics, gender)
Evidence News 21 August 2013