Today we know more than four and a half thousand of hereditary diseases, and each case has a solid evidence base that the disease is transmitted is inherited, and nothing else.But, despite the high level of development of diagnostics, not all genetic diseases are studied to the degree of biochemical reactions.However, the underlying mechanisms of hereditary diseases known to modern science.
There are three basic kinds of mutations:
fundamental genetic laws of Mendel determine the dominant and recessive genes.After fertilization, fetal cells contain half of the mother's genes and half of the father, making a pair - alleles.Genetic combinations not so much: only two.The defining features are manifested in the phenotype.If one of the mutated gene allele is dominant - the disease manifests itself.The same occurs when the dominant pair.If the gene is recessive, in the phenotype is not reflected.The manifestation of hereditary diseases transmitted by rece
chromosomal mutations manifest violation of their division during meiosis.As a result, there are additional chromosome duplication: how sexual and somatic.
sex-linked hereditary abnormalities are transmitted through sexual X chromosome.Because men it is presented in the singular, in all males in the family, there are manifestations of the disease.While women have two X sex chromosomes are the carriers of the damaged X chromosome.For displays hereditary disease in women, sex-linked, it is necessary that the patient has inherited defective both sex chromosomes.This happens very often.
Manifestations of hereditary diseases depends on many factors.The features built into the genotype, have symptoms (affecting the phenotype) under certain conditions.In this regard, biology of hereditary diseases shared by all genetic diseases in the following groups:
Sometimes, even a non-inherited disease symptoms found in children with people.This is facilitated by the same susceptibility relatives to certain factors.For example, the development of rheumatic fever, which is the causative agent has nothing to do with genes and chromosomes.Nevertheless, children and grandchildren are also subject to systemic connective tissue disorders β-hemolytic streptococcus.Many people have chronic tonsillitis accompanied by a lifetime, but does not cause genetic diseases, while having relatives with rheumatic valvular heart disease, developed a similar pathology.
Causes of hereditary diseases associated with gene mutations that are always the same: the gene defect - enzyme defect - absence of protein synthesis.As a result, the substance accumulates in the body, which should have become a necessary elements, but in themselves as intermediates biochemical reactions are toxic.
example, classical hereditary disease - phenylketonuria caused by defective gene, which regulates the synthesis of an enzyme that converts phenylalanine to tyrosine.Therefore, the brain suffers from phenylketonuria.
When lactase deficiency occurs bowel disorder.Raw cow's milk intolerance - a phenomenon quite widespread, and it also refers to a hereditary disease, although, under certain circumstances, in some people the compensation can occur, and lactase production is getting better due to active "training" intestinal cells.
Chromosomal abnormalities occur regardless of the conditions.Many children are simply not viable.But Down syndrome refers to the hereditary diseases in which external environmental conditions can be so beneficial that patients become full members of society.
Defects division of sex chromosomes are not accompanied by deadly complications, as it does not hurt the somatic symptoms.All the vital organs in these hereditary diseases are not affected.Lesions are found at the level of the genital organs, often only internal.Sometimes it does without them.For example, the syndrome of a triple-former, when a woman has extra X chromosome, fertility is maintained.And the children are born with a normal set of sex chromosomes.A similar situation with an extra Y-chromosome in males.
mechanism of hereditary diseases lies in the combination of genes: dominant and recessive.Various combination of differently manifested in the phenotype.For the development of the disease sufficiently dominant mutant gene or pathological recessive allele in one pair.
prevent the emergence of genetic diseases by specialists genetic centers.The antenatal major cities special rooms geneticists are working to provide counseling for future couples.Held prevention of hereditary diseases by compiling genealogical charts and decoding of special analyzes.
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