What is the importance of Crossing Over ?

During prophase I of melosis, a part of chromatid of one chromosome goes over to a chromatid of the other chromosome and vice versa. This interchange of the parts of the chromatids of a pair of homologous chromosomes is known as crossing over. Thus, there is an exchange of genes or the genetic material between the two chromatids.the new chromosomes is different from both the parent chromosomes.

This leads to variations in the population. Through the maternal gametes (ova) and paternal gametes (sperms), hereditary traits (characters) are passed on to child from parents. Genes are linearly arranged in chromosomes which are the carriers of hereditary traits. With the crossing over of two parental chromosome segments, a child inherits some of the traits from the mother and some from the father. This is why; two children from the same parents resemble each other in some characters and differ in others.

The process of crossing over and its genetic significance can be understood by the following diagrams. Crossing over takes place between the nonsister chromatids of homologous chromosomes (one paternal and the other maternal).

After this process, maternal chromatid picks up the part of paternal chromatid having gene sequence b and c. On the other hand, paternal chromatid obtained the maternal chromatid with gene sequence B and C. the resultant chromosome is different from the chromosoeme of either parent. In other words, the resultant chromosome possesses genes of both the parents. This results in variation in gene combinations which are reflected in the variation of characters.