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    Phenotypic Ratios

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    What are the expected phenotypic ratios for a monohybrid cross?

    For a dihybrid cross?

    For a sex-linked trait?

    See attached file for full problem description.

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    (Have added this information as an attachment as well so that you get colour!)

    From the data that you have given, I should be able to offer you some guidance regarding phenotypic ratios from standard Mendelian crosses.

    Monohybrid cross:

    Let the gene for Curly hair, the dominant allele have the symbol C and the gene for straight hair have the symbol c.

    Assuming a homozygous, pure breeding cross between a curly haired person and a straight haired person.

    i.e. CC x cc.

    Then in the first generation the F1 all of the children would have curly hair because, they would all have the genotype Cc.

    If however both had been heterozygous

    i.e Cc x Cc

    then the following possibilities arise;

    CC Cc Cc cc

    In other words there would be a ratio of 3 times as many curly haired as straight haired offspring.

    From the data that you have, this is often referred to as the backcross experiment you have a mating between the following genotypes

    i.e. Cc x cc

    This mating will give the following combinations

    Cc Cc ...