This is the consequence of the exchange of genetic material called crossing over. It is known that diploid cells carry two versions of each gene, namely, two alleles. Meiosis results in haploid gametes with only one set of chromosomes. Crossing over occurs in meiosis where homologous chromosomes pair up and exchange different segments of the genetic material. So, although they are on the same chromosome, alleles for one trait will be exchanged, and for another will not. This results in chromosomes with new combinations of genes. Without crossing over, all traits on one chromosome will be inherited together, so a parent will produce gametes with only two different combinations and genetic variation will be significantly decreased.
