Q. How Genes can be exchanged between chromatids?

When two homologous chromosomes physically exchangecorresponding segments during prophase I of meiosis, geneticists call it crossing over. Recombinations take place at chiasmata during pachytene of meiosis-I. If just a few exchanges take place, genes which are closer together are likely to stay together. The farther apart on same chromosome genes are, more likely they will separate during recombination. The two extremes are independent assortment and absolute or complete linkage. Progeny resulting from crossing over appear in repeatable proportions, known as recombinant frequency. Greater recombination frequencies are observed for genes which are farther apart on chromosomes as a chiasma is more likely to cutbetween genes which are far apart than genes that are closer together.