Linked inheritance

Such a concept as the inheritance of traits is widely studied in genetics. They explain the similarity of offspring and parents. It is curious that some manifestations of features are inherited together. This phenomenon, first described in detail by the scientist T. Morgan, became known as "linked inheritance". Let's talk about it in more detail.

As you know, every organism has a certain number of genes. The chromosome is also a strictly limited figure. For comparison: a healthy human body has 46 chromosomes. The genes in it are thousands of times larger. Judge for yourself: each gene is responsible for one or another of the signs, manifested in the external appearance of a person. Naturally, there are a lot of them. Therefore, they began to say that several genes are localized in one chromosome. These genes are called the clutch group and determine concatenated inheritance. Such a theory has existed in the scientific community for quite a long time, but only T. Morgan gave it a definition.

In contrast to the inheritance of genes that are localized in different pairs of identical chromosomes, linked inheritance results in the formation of a diheterozygotic individual of only two types of gametes, which repeat the combination of parental genes.

Along with this, gametes arise, the combination of genes in which differs from the chromosomal set of parents. This result is a consequence of crossing-over, a process whose importance in genetics is difficult to overestimate, because it allows the offspring to receive different signs from both parents.

In nature, there are three types of inheritance of genes. In order to determine what type is inherent in this particular pair, the analyzing cross is used. As a result, one of the three options listed below will be obtained:

1. Independent inheritance. In this case, hybrids differ from each other and from parents in appearance, in other words, as a result, we have 4 variants of phenotypes.

2. Complete linkage of genes. Hybrids of the first generation, obtained by crossing the parents, completely repeat the phenotype of the parents and are indistinguishable among themselves.

3. Incomplete cohesion of genes. Just as in the first case, when crossing, 4 classes of different phenotypes are obtained. At the same time, however, new genotypes are formed, completely different from the parent fund. It is in this case that the crossover mentioned above is involved in the formation of gametes.

It was also found that, the smaller the distance between inherited genes in the parent chromosome, the higher the probability of their full linked inheritance. Accordingly, the farther apart they are, the less often there is a cross at meiosis. The distance between genes is a factor, primarily determining the probability of concatenated inheritance.

Separately, it is necessary to consider concatenated inheritance associated with gender. Its essence is the same as in the variant considered above, but the inherited genes in this case are located in the sex chromosomes. Therefore, talk about this type of inheritance is possible only in the case of mammals (man among them), some reptiles and insects.

Taking into account the fact that XY is a set of chromosomes corresponding to the male sex and XX to female sex, we note that all the main signs responsible for the viability of the organism are located in the chromosome present in the genotype of each organism. Of course, we are talking about the X chromosome. Women may have both recessive and dominant genes in chromosomes. Men can inherit only one of the options - that is, either the gene manifests itself in the phenotype, or not.

Linked inheritance, due to gender, often sounds in the context of diseases that are peculiar to men, while women are only their carriers:

• hemophilia,
• Color blindness;
• Lesha-Nayhan syndrome.