Crossover

Crossover mutations are mutations in which regions are exchanged between homologous chromosomes. This occurs during meiosis when homologous chromosomes exchange regions to form crossover chromosomes.

Crossover can occur in both gametes and zygotes. In the first case, crossover chromosomes are formed as a result of the exchange of regions between two homologous chromatids, and in the second case, between two different chromatids.

In order to understand how crossover occurs, consider meiosis using the example of a pair of chromosomes. During the first division of meiosis, homologous chromosomes move to the poles of the cell. Then the second meiotic division occurs, in which homologous chromatids move to different poles.

During the second division of meiosis, areas are exchanged between chromatids of different chromosomes, which leads to the formation of crossover chromosomes. It is important to note that crossover chromosomes are not mutations, but are formed as a result of the normal process of meiosis.

In addition, it should be noted that the exchange of regions occurs not only between homologous, but also between non-homologous chromosomes, but this leads to less noticeable changes in the genome.

In general, crossovers are an important part of genetic diversity and are essential for maintaining genetic stability. However, they can also lead to various hereditary diseases if they occur in certain regions of the chromosomes associated with certain genes.

Thus, crossovers are an important element of genetic diversity that is necessary to maintain genome stability. They are formed by meiosis and can lead to hereditary diseases under certain conditions.

Crossover - in molecular genetics, these are two chromatic, that is, two homologous chromosomes that exchanged their segments during meiosis (parasynthesis). These genetic events arise as a result of the duplication of a significant portion of a chromosome and the divergence of two copies during mitotic cell divisions. Due to duplication of this region of a homologous gene, two identical alleles arise, which increases the likelihood of genotypes with overdominant action or a donor gene.

Crossover in meiosis occurs in germ cells in all eukaryotes. It occurs through the random joining of chromosomes in a pair of prophase I of the meiotic division. Two identical homologous X chromosomes from cells with spindle nuclei, for example, are separated at the same distance from the nucleolus. After this, they stand side by side inside the nuclear envelope, and