AP BIOLOGY

Detailed explanation-1: -Crossing over happens between homologous chromosomes. It happens between the non-sister chromatids of the bivalent. Crossing over between sister chromatids does not lead to new genetic combinations.

Detailed explanation-2: -Crossover occurs between non-sister chromatids of homologous chromosomes. The result is an exchange of genetic material between homologous chromosomes. The crossover events are the first source of genetic variation in the nuclei produced by meiosis.

Detailed explanation-3: -The result is an exchange of genetic material between homologous chromosomes. This occurs when homologous chromosomes align. Chromatids from each chromosome can cross over and recombine (swap sections). This results in two recombinant chromosomes and two non-recombinant chromosomes.

Detailed explanation-4: -Crossing over is the exchange of genetic materials between non-sister chromatids of homologous chromosome. It takes place at pachytene stage of prophase-I.

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.