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Homework Help: Simple Genetics question

  1. Jan 26, 2010 #1
    1. The problem statement, all variables and given/known data

    A cross between two plants that both have green flowers produces 80 offspring plants, of which 36 have green flowers, 23 have black flowers, and 21 have blue flowers. Color variation is due to inheritance at one locus. What is the genotype associated with each flower color?

    How can the inheritance of the flower color be described?

    2. Relevant equations

    Law of Independent Assortment
    Law of Segregation

    3. The attempt at a solution

    36/80 green
    23/80 black
    21/80 blue

    such numbers yield a ratio close to 1:2:1, equivalent to a monohybrid cross.

    Gg x Gg

    1 GG
    2 Gg
    1 gg

    This seems to indicate either codominance or incomplete dominance. However, in this case, the hybrids are neither a blend of their parents nor do they exhibit traits from both parents, so I'm left a little confused.

    Do I need to somehow incorporate mutations or wild type into this?
  2. jcsd
  3. Jan 27, 2010 #2
    From Scitable, Genetic Dominance: Genotype-Phenotype Relationships, under the overdominance section:

    "In some instances, offspring can demonstrate a phenotype that is outside the range defined by both parents."

    It's difficult to think of a scenario that is plausible for the phenotpye of heterozygotes. Perhaps one does not dtermine colour without the presence of the other allele. Homozygous individuals in this case may have a 'default' colour due to the presence of a molecule, A. One allele may convert A to B, and the other allele B to C. Without the allele converting A to B, the allele for B to C will not perform its function, the flower will then have the default colour in individuals homozygous for this allele. Homozygous individuals for the the other allele, will convert A to B, producing a certain colour; and heterozygous individuals will convert A to B and B to C, producing yet another colour (in this case, green). This seems plausible, but I'm not sure if it is what you are looking for.
    Last edited: Jan 27, 2010
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