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# Recombination * Recombination helps ensure proper chromosome segregation during meiosis I. * If recombination did not occur, nondisjunction during meiosis I would happen frequently. * Synaptonemal complexes help homologous chromosomes pair, but disappear during prophase I. * Chromosomes are still...

# Recombination * Recombination helps ensure proper chromosome segregation during meiosis I. * If recombination did not occur, nondisjunction during meiosis I would happen frequently. * Synaptonemal complexes help homologous chromosomes pair, but disappear during prophase I. * Chromosomes are still attached by chiasmata and cohesin, molecular complexes able to connect sister chromatids. ## Recombination Frequencies Recombination frequencies are the basic of genetic maps. * **H. Sturtevant** proposed the recombination frequencies (RF), percentage of total progeny that were recombinant types could be used as a measure of physical distance between two linked genes. * 4% RF = 1 map unit (mu) = 1 centi Morgan (cM) **Example:** * W___Y = 1.1 mu * W___M = 32.8 mu ## Recombinant Gametes Recombinant gametes are less frequent than parental gametes when genes are linked. **Examples:** * **NCOs**: Meioses with no crossing-over between A and B produce 4 parental gametes. * **SCOs**: Meioses with one crossover between A and B produce 2 parental and 2 recombinant gametes. * **Diagram of NCOs**: A circle with the following inside: * AB * aB * Ab * ab * lines connecting A and B * lines connecting a and b * **Diagram of SCOs**: A circle with the following inside: * AB * aB * Ab * ab * lines connecting A and b * lines connecting a and B