NEET BIOLOGY

Detailed explanation-1: -Definition. Crossing over, as related to genetics and genomics, refers to the exchange of DNA between paired homologous chromosomes (one from each parent) that occurs during the development of egg and sperm cells (meiosis).

Detailed explanation-2: -During prophase I, homologous chromosomes pair up and exchange sections of DNA. This is called recombination or crossing over. This is followed by metaphase I where the connected pairs of chromosomes align at the middle of the cell. After the pairs of chromosomes are aligned, anaphase I begins.

Detailed explanation-3: -When homologous chromosomes form pairs during prophase I of meiosis I, crossing-over can occur. Crossing-over is the exchange of genetic material between homologous chromosomes. It results in new combinations of genes on each chromosome.

Detailed explanation-4: -During meiosis, crossing-over occurs at the pachytene stage, when homologous chromosomes are completely paired. At diplotene, when homologs separate, the sites of crossing-over become visible as chiasmata, which hold the two homologs of a bivalent together until segregation at anaphase I.

Detailed explanation-5: -Pairing of homologous chromosomes is a fundamental event in meiosis, where it is normally accompanied by high levels of genetic recombination and results in the segregation of homologs into separate cells. However, homolog pairing can also occur in a variety of other contexts.