crossing over during meiosis allows recombination of genes between homologous chromosomes this alters the linkage between genes on the same chromosome crossing over occurs frequently during prophase one of meiosis when homologous chromosomes associate with each other in a structure called a tetrad first consider the possible inheritance of alleles for two genes on a particular chromosome when crossing over does not occur recall that one member of each pair of homologous chromosomes came from one parent the other member came from the other parent in this example one parental chromosome had alleles capital a and capital b while the other had alleles lower case a and lower case b without crossing over each haploid cell produced will inherit a chromosome with the same combination of alleles as was on one of the parental chromosomes thus the arrangement of linked genes is not altered in this case now consider the case where there is crossing over in the region between the two genes since the crossing over is only between two individual chromatids the possible haploid cells after meiosis have four different genetic combinations two will come from the chromatids that did not participate in crossing over and thus will still have the parental combination of alleles either capital a and capital b or lowercase a and lowercase b the other two will be recombinant with either capital a and lowercase b or lowercase a and capital b alleles thus crossing over allows for the reassortment of linked genes