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    Punnett Squares and Pedigrees

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    Consider the following five family pedigrees below chosen for study because: 1) two rare conditions are segregating; scaly elbows (X symbol) and a liver disease (filled symbol). 2) the families are large in size.
    a) What is the mode of inheritance of scaly elbows?
    b) What is the mode of inheritance of the liver disease?
    c) Use symbols to describe the genotypes of all five sets of parents.
    d) Do you see evidence of linkage? Quantitative if possible. (Careful, not every family may be informative here)...

    (See diagram in attachment)

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    Solution Preview

    For every question, you'll need to know the number of female and male children with each phenotype:
    Scaly liver both Normal Total
    Females 10 0 0 6 16
    Males 4 6 5 6 21
    Total: 14 6 5 12 37

    a) A good place to start is generally to determine whether the trait may be X-linked. Do males seem to be more affected than females (if so, this would suggest an X-linked recessive trait)? Since the male:female ratio for this phenotype is 9:10 (or approximately 1:1), this does not appear to be the case (note that you must add the number of "scaly" and "both" males to get the right number of males with the scaly phenotype). The over-all ratio of affected to unaffected is also approximately 1:1. If this is not an X-linked trait, then the problem is not informative enough to determine whether it is dominant or recessive, as crossing a ...

    Solution Summary

    The expert examines Punnett Squares and Pedigrees for families.