AP BIOLOGY

Detailed explanation-1: -In meiosis I, during pachytene, crossing over occurs between the non-sister chromatids of the homologous chromosomes. The exchange of genetic material (DNA) between the non-sister chromatids of the homologous chromosomes is known as crossing over.

Detailed explanation-2: -Crossing-Over. Crossing-over occurs during prophase I, and it is the exchange of genetic material between non-sister chromatids of homologous chromosomes.

Detailed explanation-3: -Non – sister chromatids are a pair of homologous chromosomes having different alleles. When crossing over occurs chiasma is formed which is the point of contact between the non-sister chromatids which results in the exchange of genetic material.

Detailed explanation-4: -Chiasmata is the point at which two homologous non-sister chromatids exchange genetic material. Chiasmata represents the site of crossing over.

Detailed explanation-5: -Non-sister chromatids are used to demonstrate crossing over because if sister chromatids did go through crossing over, they would be sharing the same/practically identical genetic information with each other, which is not the purpose of crossing over.