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    Genetic map of 3 linked genes found on the same chromosome

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    In corn, the following recessive genes have been identified on chromosome 3:

    yg = yellow green seedlings
    wx = waxy endosperm
    bz = bronze color

    From a three point testcross between plants heterozygous for all three genes and plants homozygous recessive for all three genes, the following data were obtained:

    yellow green 6
    yellow green, waxy 720
    wild type 56
    bronze, waxy 13
    bronze 681
    yellow green, bronze 25
    waxy 31
    yellow green, bronze, waxy 42

    a. Which gene is in the middle?
    b. What is the distance between genes yg and wx?
    c. What is the distance between genes wx and bz?
    d. What is the distance between genes yg and bz?

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    Solution Summary

    When genes are found on the same chromosome they are called linked genes. By examining the recombination frequencies between these genes during a three-point test cross you can determine how far apart the genes are from each other. This is called a gene map. This explanation will walk you through how to examine the data provided by a three point cross to determine what the distances are between each gene. Once the distances are known the explanation then describes how to put the genes in the correct order they would be found in on the chromosome.