Assertion (A): Genetic variability is the root of any breeding programme.

Reason (R): In sexually reproducing organisms crossing over and chiasmata formation occurs between non-sister chromatids of homologous chromosomes.

The assertion is generally true. Genetic variability refers to the presence of genetic differences within a population. In the context of breeding programs, genetic variability is essential because it provides the raw material for selection and improvement. Breeding programs often aim to create or enhance desirable traits in plants and animals. Without genetic variability, there would be no basis for selecting individuals with the desired traits to produce the next generation. So, genetic variability is indeed a fundamental requirement for the success of breeding programs.

The reason is also true. Crossing over and chiasmata formation are processes that occur during meiosis, which is the cell division process that leads to the formation of gametes (sperm and egg cells) in sexually reproducing organisms. During meiosis, homologous chromosomes (chromosomes with the same genes, but potentially different alleles) pair up, and crossing over involves the exchange of genetic material between non-sister chromatids of these homologous chromosomes. This results in the creation of new combinations of alleles, increasing genetic diversity among the gametes.

In summary, both the assertion and the reason are correct, but they are not directly connected. Genetic variability is indeed crucial for breeding programs, and crossing over during meiosis is one of the mechanisms that contributes to genetic diversity in sexually reproducing organisms. However, the reason does not explain or support the assertion directly.