BIOL 2500 Lecture Notes - Lecture 9: Harriet Creighton, Synteny, Reginald Punnett
9 Feb 2017
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Creighton, mcclintock and stern showed that crossover is accompanied by chromosome breakage and rejoining. In early prophase 1, points of crossing over are established at recombination nodules along the synaptonemal complex. Genes that are close together are less likely to have a recombination nodule between them than genes farther apart. Upper limit to recombinant gametes - single crossovers. Crossing over occurs after replication at the four-strand stage. Single crossovers involve ne chromatid from each homolog. In each case, two recombinant and two parental gametes are formed: thus when single crossovers occur, the result is 50% recombinant gametes and 50% parental, draw. Upper limit to recombinant gametes - double crossovers. When all combinations of single and double crossovers are summed, the maximum proportion of recombinant gametes that can be produced is 50% Most instances of genetic linkage yield frequencies lower than this.
