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Biology LibreTexts

7.S: Linkage and Mapping (Summary)

  • Page ID
    4103
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    • Recombination is defined as any process that results in gametes with combinations of alleles that were not present in the gametes of a previous generation.
    • The recombination frequency between any two loci depends on their relative chromosomal locations.
    • Unlinked loci show a maximum 50% recombination frequency.
    • Loci that are close together on a chromosome are linked and tend to segregate with the same combinations of alleles that were present in their parents.
    • Crossovers are a normal part of most meioses, and allow for recombination between linked loci.
    • Measuring recombination frequency is easiest when starting with pure-breeding lines with two alleles for each locus, and with suitable lines for test crossing. 
    • Because recombination frequency is usually proportional to the distance between loci, recombination frequencies can be used to create genetic maps.
    • Recombination frequencies tend to underestimate map distances,  especially over long distances, since double crossovers may be genetically indistinguishable from non-recombinants.
    • Three-point crosses can be used to determine the order and map distance between of three loci, and can correct for some of the double crossovers between the two outer loci.

    Key Terms

    linkage

    recombination

    independent assortment

    crossover

    recombinant genotype

    parental genotype

    unlinked

    recombination frequency (RF)

    complete (absolute) linkage

    incomplete (partial) linkage

    syntenic

    synapsis

    coupling (cis) configuration

    repulsion(trans) configuration

     

     

    repulsion

    map units (mu)

    centiMorgans (cM)

    genetic map

    conserved synteny

    double-crossover

    three-point cross

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