The pairing of homologous chromosomes during prophase 1 lets the crossing over to occur and crossing over between non-sister chromatids, in turn, lets the recombination to occur. Crossing over occurs at points called chiasma, which are created between non-sister chromatids. Chiasma lets the exchange of DNA segments between non-sister chromatids. This exchange of DNA segments produces new combinations of alleles among the offspring, which is identified as genetic recombination.
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