Solution

Crossing over is the process of exchange of genetic material between non-sister chromatids of homologous chromosomes to produce new genetics combinations or variations; it is dependent on the distance between the genes of chromosomes, purity or heterozygosity of parents do not affect it which makes option D incorrect. Recombination is the random fusion of gametes; crossover and recombination produce visible recombinant phenotypes which make option C correct. Mendel chose seven pairs of contrasting traits, the gene for each of which is present on seven different chromosomes of pea plant which makes option B incorrect. Due to the presence on different chromosomes, Mendel's trait followed independent assortment during meiosis and produced the expected parental and recombinant phenotypes. If genes of these traits would have presented together showing linkage, Mendel would not have got the expected results. The correct answer is A.