ristikkäistymisprosessi

Ristikkäistymisprosessi, often translated as crossing-over or recombination, is a fundamental biological process that occurs during meiosis, the specialized cell division that produces gametes (sperm and egg cells). This process is crucial for genetic diversity within a species. It involves the exchange of genetic material between homologous chromosomes, which are pairs of chromosomes that carry the same genes but may have different alleles.

The process begins in prophase I of meiosis when homologous chromosomes pair up. At specific points along these paired chromosomes, called chiasmata, the non-sister chromatids (one from each homologous chromosome) break and then rejoin, swapping segments of DNA. This exchange shuffles the alleles of the genes located on those chromosomes. As a result, the resulting chromatids in the daughter cells are mosaics, carrying combinations of alleles that were not present on the original parental chromosomes.

This genetic shuffling is a significant driver of evolution. It ensures that offspring inherit a unique combination of genes from their parents, increasing the variability within a population. This variability is essential for adaptation and survival in changing environments. Without crossing-over, offspring would inherit chromosomes that are exact copies of their parents', greatly limiting genetic diversity and the potential for evolutionary advancement.