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    Determining phenotypic ratio using test crosses

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    A true-breeding red snapdragon was crossed to a true-breeding white snapdragon. The F1 progeny were pink. When F1 x F1 matings were made, the following F2 progeny were observed.

    1850 red
    670 pink
    831 white

    Total 3351

    a. Using clearly defined genetic symbols, give the appropriate parental, F1 and F2 genotypes in order to explain the above results.

    b. What phenotypic ratio would be expected from a testcross of an F1 snapdragon

    c. Suppose the white phenotype is now lethal. What phenotypic ratio would be expected from a cross between F1 individuals?

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    Solution Preview

    a) Use W for red flowers and w for white. The plants are true breeding meaning they have to be homozygous (WW and ww). Therefore the first cross is...

    WW x ww

    f1 is all pink, with the genotype Ww.

    The reason the plants appear pink is that w is co-dominant to W. Therefore any plants that are Ww appear pink. Snapdragons are known to exibit this trait. Plants that ...

    Solution Summary

    This solution helps determine the phenotypic ratio using test crosses.