Updated: 5/4/2017

Gene Mapping

Review Topic
Linkage Analysis
  • Principles
    • linkage
      • the rate of cosegregation of two syntenic alleles (alleles appearing on the same chromosome) is inversely proportional to the distance between the alleles
        • i.e. genes that are physically close on a chromosome will be inherited together more often
        • genes that are physically far apart will be inherited together less often
    • linkage group
      • set of genes at different loci on the same chromosome that tend to act as a single set of genes in meiosis rather than undergoing independent assortment
        • an exception is if crossing over occurs
    • linkage analysis
      • using a pedigree to determine the location of an allele based on the rate of cosegregation with other alleles of known location (genetic markers)
      • can be used to track disease-causing mutation
        • linkage analysis can localize a gene responsible for a trait when the sequence is unknown
    • centi-Morgan (cM):
      • a unit used to measure genetic linkage
      • a length of DNA over which the frequency of homologous recombination is 1%
        • 1% chance that a marker on a chromosome will become separated from a second marker on the same chromosome due to crossing over
        • two loci that are 1 centimorgan apart will experience recombination between these two loci in 1% of meiosis.
    • parental gamete
      • the portion of chromosome looks the same as that of one of the parents
      • no recombination 
    • nonparental gamete
      • homologous recombination has occurred in the region of interest 
    • linkage disequilibrium
      • when alleles occur together more often than can be accounted for by chance
        • indication that 2 alleles are physically close together


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