Sex-Linked Inheritance

N. trait - characteristics, the state of the body and the ability to reproduce, are controlled by genes located on the sex chromosomes. Features of heredity based on sex-linked traits are that genes are inherited regardless of which sex chromosomes were received from parents. Genes located on the sex chromosomes are called sex-linked. For example, the gene for hypocholesterolemia is inherited in both women and men, and the gene for color blindness is inherited only by men. Because of this, sex-linked diseases are more susceptible to treatment and prevention. Thus, the disease endocarditis, in which rupture of the heart valves is possible, can only affect men. Examples of other diseases not found in women include hemophilia and muscular dystrophy. Neuropsychiatric diseases include insulin insensitivity (diabetes), one of the most common autoimmune diseases. It is diagnosed when no antibodies have been produced in any of the standard tests against blood insulin. In humans, there is an uneven distribution of recessive genes. In women, a pair of autosomal male genes potentially contains three autosomal normal forms and only one recessive gene. The recessiveness of the gametal gene without duplication of the autosomal one is 1 to 4, while the manifestation of the recessive gene is 25%. In males, gene recombination results in a more equal distribution, with 3 or 4 elements from each group produced in eight gametes. And in about 5% of cases, random genetic covalence of alleles occurs, leading to the appearance of heterozygotes. Thus, through recombination, a mutation may have a better chance of surviving in the entire gene pool of a population. If all phenotypes are recessive, then homozygosity will manifest itself in heterozygotes either in most cases or absent. In the first case, these genes become determining factors of somatic development, and the second generation of descendants will produce them. When a recessive trait is not decisive, its manifestation is possible in a heterozygous state. In this case, in subsequent generations, the two types of allelic genes are produced with equal frequency. For this reason, with the same frequency of recessing genes in individual pairs of chromosomes, the magnitude of deviations from the norm will be greater. This is due to the fact that such genes influence a fairly wide environment inside cells - they interact with hemoglobin. Autosomal recessive mutations are those that, if present, lead to expression of the gene program even in the absence of mutations in the reproductive apparatus, that is,

Sex-linked inheritance is a form of genetic inheritance in which one of the parents is the carrier of a gene that determines a certain trait, but its manifestation depends on the sex of the child. At the same time, the genetic structure of the parents does not affect the appearance of this trait in the offspring, i.e. Only the gene is inherited, not the trait itself.

Let us consider the mechanism of linkage of a gene and sex chromosomes using the example of human Mendelian traits, which are formed due to the linkage of genes with the X and Y chromosomes. All sex-related traits are inherited according to the laws of Mendelian crossing over. Normally women have four