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Damage to DNA
25 Nov 2016
Biophysicist Dr. Doping tells about mutations in the genome, Queen Victoria and Tay Sachs desease. What is DNA damage and how it happens? How many mutations appears annually at the man in the genome of the sperm? As Queen Victoria damaged chromosome influenced the Russian history?
The process of doubling or replication, DNA extraordinarily accurate. DNA polymerase - absolutely wonderful enzymes that manage to synthesize new DNA strands on the principle of complementarity with amazing accuracy. Errors occur with quite a negligible probability. But they still occur - in such insanely long molecules that we have in our body, in DNA molecules. Thus, DNA damage occurs, an error occurs and the error is, of course, extremely important to us. The genetics of these errors are called mutations.
Geneticists it is known a very long time. Even before the discovery of DNA structure genetics knew that mutations occur in the genes. But they did not know what exactly these mutations are expressed, what happens specifically in such cases. Now that we have learned to read the DNA sequence, we know all the details of what happens to the DNA molecule in such troubles as mutations. Examples are a great many, but I'll talk about some that I think are the most impressive.
Cyanocobalamin injection (Vitamin B12) - is extremely essential for making DNA synthesis.
Almost all the XIX century in the UK rules of Queen Victoria, this period is even called the Victorian era. Few people know that in addition to longevity and good health Queen Victoria had its genome a replacement unit. One unit of three billion was replaced. This damage inherited from her father, who begot her, when he was 50 years old. It's not a very good idea - to have a child at this age. The fact that men with age occurs the accumulation of DNA damage occurs because spermatogenesis in men throughout life. Now it is investigated thoroughly quantified: we know that on average, each year there are two additional mutations in the genome of the sperm. Therefore, to the 50 years of accumulated, it is easy to calculate a decent amount of mutations. And when you consider that we have a baseline of about 14 mutations on average, it is a great gain - say, 60 additional mutations.
These mutations occur at exactly the transformation of germ cells, because most errors occur during replication during meiosis when gametes are formed. Now we know that Queen Victoria received a mutation from their fathers, this mutation is associated with the X-chromosome. Let me remind you that we have normal chromosomes called autosomes and the sex chromosomes - men is the X- and Y-chromosomes in females is two X-chromosomes. So Queen Victoria received from mum and dad on the X-chromosome, and from the pope, she received X-chromosome damage. Why moms age does not matter? First, mothers are usually younger, but not the main thing. The main thing is that girls, women all germ cells, all of the egg formed very early and once and for all, on the rest of his life.
For the entire period of reproduction women have eggs that are formed even in the embryonic stage.
So they always have about 14 violations. And men it increases with age. Therefore, we believe that it is the pope gave Queen Victoria the damaged X-chromosome.
Damage was that it was flawed gene responsible for blood clotting protein, but if there are two X-chromosomes, it does not manifest itself. At most of Victoria and all the women who received from her damaged X-chromosome, it did not show. But as soon as the boy with this X-chromosome, has a different chromosome Y, then, it means that it generally does not produce clotting factor. And it turns out the disease, which is called hemophilia. This gene Queen Victoria gave her granddaughter, who became Tsarina Alexandra Feodorovna - the wife of Nicholas II, the, and she gave birth to the heir Alexei, who was a hemophiliac. Because of this, to the court was brought by a charlatan Rasputin names because this has occurred, in particular, the Russian revolution. This caused great indignation among the various segments of the population - that this quack was brought to the court. Of course, the Russian Revolution are many reasons, but one of them is genetic.
Another example of genetic diseases - so-called Tay - Sachs disease, which occurs mainly in Ashkenazi Jews. Ashkenazi Jews - a European Jews, who said at one time in Yiddish, that is a dialect of the German language, and they come from Germany. All Eastern European Jews are descendants of Ashkenazi Jews. They increased for accidental reasons presence damaged gene that causes Tay - Sachs. This is a terrible hereditary disease - a child dying by about 4 years. This is a very unpleasant thing. And the probability of occurrence of the disease among Ashkenazi Jews is 100 times higher than among the general population. It belongs to the category of the so-called Jewish diseases.
It was a terrible scourge for Ashkenazi Jews, and advances in the science of DNA have allowed to develop completely reliable methods of diagnosis of these genes, and genetic counseling has become to allow couples who are going to start a family, to decide whether they want to do it or not, because the genetic analysis says they both say, are carriers of the gene. If both are carriers of the gene, then this is an autosomal disease, autosomal mutation not sex chromosomes. Therefore, in order to make it apparent you need to both chromosomes, and that came from his mother, and from the pope, carried the bad gene. This faulty gene must come from both parents. It is easy to calculate that if both parents are carriers of the gene, then with probability ¼ child is sick, he has in both chromosomes is damaged gene. It is a high probability, and therefore often the bride and groom refused to marry, if such a situation is provided so as not to face such problem. Particularly acute, this problem in the religious Jews, because they have banned abortion, they usually have many children for the same reasons, are prohibited not only abortion, but also contraception. Therefore, they have a very high probability of at least one child that they are going to start to be sick, and it is a tragedy for the family.
As a result, even the rabbis refuse to enter into marriage until the bride and groom did not bring a certificate that they have passed a genetic consultation. They decide they will marry or not, but they should know what to expect. This led to what is now a disease Tay - Sachs disease among Jews is less common than among the general population. It is understood that the disease gene is present in Jews at the same concentration, but meeting these two genes arose to disease is now almost eliminated. This achievement is the science of DNA and developed as a result of the methods of science of genetic analysis.
