Question

crossing over is the exchange of genetic material between
A. Non-sister chromatids of the homologous chromosomes
B. Sister chromatids of the homologous chromosome
C. Chromatids of non-homologous chromosome
D. The genes those are completely linked

Answer 1

Hint: Crossing over also known as Chromosomal crossover, is the process of exchange of genetic material during sexual reproduction between the two homologous chromosomes also recognized as non-sister chromatids that further results in recombinant chromosomes.

Complete answer:
Option – A – Non-sister chromatids of the homologous chromosomes
Non-sister chromatids are chromatids of homologous chromosomes. Non-sister chromatids are the chromatids of the homologous chromosome, they may contain different alleles. Every chromosome has a homologous pair, one belonging to mother (maternal) and other belonging to father (paternal), these homologous pairs containing the same genes but may not contain same alleles, there are not exact copies of one another they are called non-sister chromatids.
Option – B – Sister chromatids of the homologous chromosome
A sister chromatid term is used to describe the identical copies of chromatids formed by the DNA replication of a chromosome, with both copies joined together by a common centromere. The Homologous chromosomes might or might not be exactly the same as each other because they derive from different parents.
Option – C – Chromatids of non-homologous chromosome
Homologous chromosomes are not the same as well as they do not originate from the same organism, they are different from sister chromatids.
Option – D – The genes those are completely linked
 Genes that are so close together on a chromosome that they are always inherited as a single unit show a relationship are considered as complete linkage. The two genes that are completely linked can only be differentiated as separate genes when a mutation occurs in one of them.

The right answer to the question is option A – “Non-Sister chromatids of homologous chromosomes”.

Note: The non- sister or non identical chromatids leads to the recombination of genetic material which involves an equal exchange. It takes place by breakage as well as the reunion of chromatid segments.