In humans, as in all other mammals Geschlechts'chromosomen determine whether the offspring will be male or female. There are two Geschlechts'chromosomen in mammals, X and Y mentioned. The Y chromosome is inherited only from father to son. Each individual inherits an X chromosome from the mother and the father is either a Y-chromosome or an X chromosome. An individual with two inherited X chromosomes is female and an individual with one X chromosome and one Y-chromosome is male. Actually you would have to already be known from school. But from the facts to which I remind you here so far, there are some conclusions that biologists and physicians are very familiar. It is time that you learn them well.
Because men have only one X chromosome, it can be no genes from which it takes two to heal, or even be viable. Such genes are not on the Geschlechts'chromosomen, but on the autosomes, wherein it is all the other chromosomes. It follows that a woman really needs only one X chromosome. Because she has won two of them, one of which is not used, but to save space so densely packed that it can be seen in some cells under a light microscope as a so-called Barr body that lies within the nucleus. Whether it's at by the father or the mother's X chromosome is inherited, is usually not care. Therefore, every cell chooses randomly one of the two. Why is statistically in every woman in half of their cells that inherited from the mother and the other half of their cells the X chromosome inherited from the father active. From here start the really interesting conclusions. Suppose that on one of the two X chromosomes, a gene is defective. This is nothing more than a genetic disease that is inherited on the X chromosome. In the case of the defective gene is not active in half of all cells of a woman, but replaced by the intact gene from the other X chromosome. If not, the cells with the defective gene are viable, they will even necessarily replaced by other cells in which the intact gene is active. It follows that the hereditary disease in the affected woman is not at all weak to strong. You will not suffer. But they can pass on the hereditary disease and seen but statistically in half the cases (not the half of the cases of affected women, but half of their children), either because they are the X-chromosome of her father or her mother passed on. Is it the hereditary disease but continued to a daughter, then suffering from the hereditary disease and also not pass it on again only to half of their children. This die inherited diseases are inherited through the X-chromosome and the maternal line, from gradually. This is especially true in societies with low birth families.
other hand, a defective X-chromosome and the associated genetic disease, however, could be inherited via the paternal line. In the case keep the male offspring spared because they are of the father's side only a Y chromosome, but received no X-chromosome. At the point we come to the main conclusion. If a couple wanting a child an X-linked inherited disease before, then you should think twice about the sex of the child and it would be justified to take effect. Only a child would be male and inherited the defective X chromosome from the maternal side, would be fully affected by the hereditary disease. The problem arises only if both parents have faulty X-chromosomes. Then the choice of partners from evolutionary point of view was suboptimal.
Nature knows of course much longer than we inherited diseases that can be made to disappear in this way and that this only works in X-linked inheritance. From this they drew conclusions and a further result of evolution is that genes important especially if one does not need two of them, were placed on the X chromosome. This in turn implies that male children inherit the defective X-chromosome, often very early or more often die before their birth. If they live after their birth, they are often mentally retarded, because on the X chromosome, many are for the development of the central nervous system relevant genes (and that has nothing at all intelligence to do so, but that often leads to exactly the wrong conclusion). This reinforced the effect can be that defective genes eliminated from the succession, by being located on the X chromosome. This in turn reinforced to accommodate the trend of evolution, particularly important genes on the X chromosome. Wherever it was set up nature, women are hardly affected by hereditary diseases, and men are affected wegselektioniert. As it is envisioned by the natural function of women to bear children and nurse, it is the real to worry by nature intended task of the men of intact genes by withstand the selection pressure and possibly in time to die (perhaps pass, therefore the male penchant for armed or otherwise dangerous occupations?) before they come into the temptation of defective genes. In fact, it is that most previous stillbirths and Disposals (observed and unobserved) are males. In areas with poor medical care and high infant mortality because of the dead, most children are also male.
result is also the conclusion that better medical care is a part on the benefit of the male children and also to maintain the most terrible hereditary diseases contribute. reach at a natural child mortality rates much more female than male individuals, the sexual maturity. Among primitive peoples rates were observed for up to twenty to one (but only where it was at the same tropical diseases), but are so uninfluenced primitive peoples no longer exist. Because such a relationship still is, to the people much better suited than today's standards, are explained by the appreciation, the male offspring in many cultures, learns the importance of the male offspring in the Hindu and Confucian religion, indirectly In many places the practice of abortion of female offspring and the Islamic rule that a husband can have four wives. Nature thus reached a gender ratio and even, by ensuring a much greater probability of male offspring than female witness. Even today, it really needs no more men to ensure healthy genes. But so-called medical progress provides more men. Nature tries to counteract, but it is not fast enough. You could change the sex ratio in Germany for births since the second world war by only one hundred and seven males to one hundred to one hundred and five female male to one hundred females. Thus it is even a surplus of men (up to the ages, in which then the longer lifespan of women to comes to bear, but that does not matter for reproduction). Which there is not only in Germany but in all industrialized countries. In areas where sex-selective abortion is practiced, there are up to one hundred and thirty male births to female hundred. This and (to an earlier time in history even necessary) polygamous cultures there is a severe lack of women, which is spread by migratory flows slowly across the globe. There was such a strong lack of women there has never been throughout history. Humanity is not adapted to it. This is not just a problem of men have come too short or aborted girls. This is a Problem that affects really all about women because many times wars were fought. Already one of the earliest and most famous wars in history, the Trojan War is said to have been led by a woman! to take action against sex-selective abortion is therefore recommended as the minimum of all peacekeeping warmly.
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