What is crossing over in meiosis?

Crossing Over in Meiosis

Crossing over is a crucial process in meiosis that results in genetic recombination, leading to increased genetic diversity in offspring. It occurs during prophase I of meiosis I, specifically at the pachytene stage.

During crossing over, homologous chromosomes, which are chromosome pairs (one from each parent) that have similar genes, align precisely with each other in a process called synapsis, forming a tetrad or bivalent. The arms of the homologous chromosomes become tightly intertwined.

At certain points along the tetrad, the non-sister chromatids (chromatids belonging to different chromosomes of the pair) break and exchange corresponding segments. These exchange points are called chiasmata.

The segments that are exchanged contain genes, meaning that the resulting chromosomes now have a different combination of alleles (versions of genes) than either of the original parental chromosomes.

The frequency of crossing over between two genes is proportional to the distance between them on the chromosome. This principle is used to create genetic maps.

Crossing over is essential for generating genetic variation, which is vital for the adaptation and evolution of species. Without crossing over, offspring would only inherit combinations of genes that were present in the parental chromosomes, limiting the potential for new and beneficial traits to arise.