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the Heredity

Вcе we know that children are often similar to the parents, grandfathers and grandmothers, brothers and sisters. But whether it is possible preduga to give their appearance till a birth? Thorough studying nasledstvennostimozhet to answer on this question.

When tell "ѕ it eyes ьр=хЁш" it is a question of a heredity, or, being expressed by a language of science, about genetics - a science studying genes.

Possibly, most exact definition of genes - biochemical codes. The sizes of genes are so small that they cannot be made out even by means of an electronic microscope. They are a part of chromosomes - visible in a microscope of the tiny threadlike structures which are in the center of a kernel of each cage of a human body. In common these structures make the full chemical scheme of the person.


Pair chromosomes

At each of us of 46 chromosomes making 23 steams which one element undertakes from spermatozoida the father, and the second - from jajtsekletki mothers.

Both elements of each pair though are very similar, but are not completely identical. At women 23 pair chromosomes, and at men one (the sexual chromosome) differs from others. If at women two big crosswise H-chromosomes, at men one of them - small krjuchkovidnaja a Y-chromosome. This insignificant difference in a cage structure defines a sex of a child. Such association of chromosomes in steams extremely important for the heredity mechanism as each pair contains similar genes, and the most simple form of a heredity mozhnoprosledit to separate pairs of genes.

There are two different kinds of genes: prepotent and retsessivnyj. Usually prepotent genes of the person even if they are present at the single copy. However that were showed identical retsessivnye genes, their pair - on one from each of parents is necessary already.


the One-factorial heredity

Genetics identified various prepotent and retsessivnye genes. For example, the gene responsible for a curly hair, is prepotent, therefore if the child inherits it, say, from the father, and a gene responsible for a straight hair (retsessivnyj), from mother it will have curly hair.

In practice not always it is possible to foresee, whether your child from you will inherit a curly hair. Actual transfer of genes by right of succession has casual character, and the prepotent gene of a curly hair has hardly more chances to be inherited. But this principle always works in the opposite direction: you cannot count that the child will have straight hair, if at one of parents they twisted, and at another straight lines.

This concerning a simple kind of a heredity is called as one-factorial. Thanks to it we receive the important and encouraging enough information on what will be the general state of health and shape of our children because, fortunately, the majority of characteristic features depends on prepotent genes. However, it not always so.


the H-factor

H - and Y-chromosomes define a sex of person, but in the H-chromosome other genes which do not have any relation to sexual signs contain also. Them name the genes linked to a floor as they are inherited with a sexual chromosome. One of such genes is responsible for ability of the person to distinguish colour. For example, red and green colours "Ёрчышёр¦=ё " a gene which is present only in the H-chromosome. The normal colour perception is prepotent line, and daltonism (inability to distinguish colour) - retsessivnoj. If the man at its unique H-chromosome has this abnormal gene, it will be the colour-blind person as for a corresponding normal prepotent gene there is no place. However if the woman inherits a daltonism gene, it chokes with a normal gene of its second H-chromosome unless to it very much will not carry, and she will inherit an abnormal gene from both parents.

As the man transfers the H-chromosome of the daughter, and a Y-chromosome to the son, daltonism is not transferred to the last. If the son is born the colour-blind person he has inherited this lack from mother - the carrier of an abnormal gene. If at mother the normal colour perception, this gene is present at one of its H-chromosomes whereas another contains a normal prepotent gene. However the daughter of the colour-blind person inheriting from it the H-chromosome, will be the carrier of an abnormal gene.

The Hemophilia (the rare disease caused nesvertyvaemostju of blood) - one more connected with a floor retsessivnaja the line defined by the H-chromosome. The woman can be the carrier of this gene, and illness is always transferred to the child of a male. Girls suffer this disease, only if they inherit this gene both from the father, and from mother. Retsessivnye genes (both normal, and abnormal) can be present at a human body but so never and not to have an effect for all his life. Besides, they pass from father to son and can be shown at any moment in a hereditary chain.


Mutirovannye genes

At once there is a question: whence undertake mutirovannye genes? Most likely, their occurrence has casual character. At early stages of development of sexual cages (man's spermatozoidov and female jajtsekletok) chromosomes are accurately copied during chemical process. Considering that this process repeats millions times and that millions chemical substances participate in it, errors are inevitable. Even simple change of a sequence of these substances leads to change of the information coded in genes. If then such change is transferred during fertilisation, and the offspring survives, it will be reproduced again and again at successors. This phenomenon is known as a gene mutation.

Mutations - the casual phenomena, and as all accidents, they can be good or bad. Unfortunately, so far as concerns such difficult and fragile creation as the person, changes as pra twisted, conduct to deterioration.

During evolution many negative changes are eradicated. Or the child dies to or at the time of delivery, or the sort gradually dies out. However some mutations, actually, are advantage: in this case "ьѕ=рэ=№" succeed at the expense of the "эюЁьрыіэ№§" fellow tribesmen, also there comes the following coil of evolution.


External threats

Natural rates of a gene mutation are very low, but some chemical substances or radiation can sharply accelerate them. The greatest danger is represented by X-rays and radioactive deposits, therefore it is not recommended to do rentgenografiju a fruit in a womb of mother, and also jaichnikov and jaichek. Austerity measures on protection of people from nuclear and other kinds of dangerous radiations Should be accepted. But the growing quantity of diseases by a leukaemia at children living near to atomic power stations, says that safety measures are insufficient. Besides, we are defenceless before space radiations, we are exposed to influence of other sources of natural radiation, including the radioactive elements containing in food and soil. All it promotes acceleration of natural rates of a mutation.


Krossingover

Though the mutation - a unique way of formation of new genes, is available for the nature a smart method of a reshuffle of genes in steams of homologous chromosomes (one from mother and one from the father). Such reshuffle thanks to which the number of gene combinations and, hence, a variety of individuals repeatedly increases, occurs during time mejoza (so scientists name process of division and reproduction of cages) and is called krossingoverom.

Krossingover often happens salutary, but can sometimes go an incorrect way and then some chromosomes receive superfluous elements, as in case of illness of Down, when in an oosperm of 47 chromosomes, instead of 46, as usually. Illness of Down is found out in one of 700 newborns, especially at late sorts. At sick children flat features, they mentally retarded or experience difficulties at training.


Penetrantnost

The Problem of hereditary defects is aggravated with that force of genes is shown not only in domination over other genes, but also in the degree of their penetration named genetikami penetrantnostju.

Penetrantnost happens weak and strong. For example, the reason of such defect of fingers as kamptodaktilija, the prepotent gene transferred at an one-factorial heredity is. However degree of display of this defect can be different - from small mobility of all fingers (full penetrantnost) to inflexibility only one finger (partial penetrantnost).

Whether the child Will inherit a hemophilia, depends only on one pair genes, but pe redacha ponasledstvu such qualities as, for example, growth or intelligence, is so difficult that cannot be supervised by single genes. These changeable qualities are actually supervised by a number of simultaneously operating genes named polygenes. Each gene brings the contribution to the general result.


Polygenes

Many lines supervised by polygenes (for example, growth, weight, colour of a skin), can strongly change depending on an inhabitancy of the person. The quantity and a kind of absorbed food influence our growth and weight, and the skin darkens under vozdejst viem solar beams. Clearly that genes and environment operate in common at formation of the human race, capable to adapt for the most different living conditions: from a cold of polar areas and a permafrost to scorching heat of desert Sahara.

Environment plays the role and in acquisition by the person of talent, for example, musical, and in its further display in a sort. It is not known that is thus inherited, and that grows out of education. There is opened a question: what part of ours " " it is put in genes and what is generated by external conditions?