Erin asked in Science & MathematicsBiology · 7 years ago

Simple Punnett Square Biology Question?

Joe Schmoe cannot taste PTC, but both his mother and father can. Do a Punnett square to calculate the expected phenotypic ratio among Joe's siblings.

What I don't understand is what to put in the punnett square...because we don't know his parents genotypes.

3 Answers

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  • 7 years ago
    Best Answer

    Ah, but you DO know his parents' phenotypes! This type of simple punnett square problem assumes conditions of complete dominance, that is: AA and Aa = can taste PTC, aa = cannot taste PTC

    Because offspring inherit one allele from each parent, the only way Joe can have the aa genotype when both his parents can taste PTC, is if both parents are heterozygous (Aa). Therefore, just set up a standard heterozygous cross Aa x Aa to calculate sibling phenotypic ratios. It should come out to a 1:2:1 ratio of AA:Aa:aa genotypes and a 3:1 ratio of Can taste PTC:Cannot taste PTC phenotypes.

    Source(s): Molecular Biology/Biotechnology major
  • feagle
    Lv 4
    3 years ago

    Simple Punnett Square

  • 3 years ago

    "Hetero" skill diverse, so the two mothers and fathers would be genotype Bb. once you do a Punnett sq., the gametes the mummy can produce bypass alongside the ideal of a container, and those the daddy can produce bypass alongside the left area. thus, the two mothers and fathers could produce 2 styles of gamete, with the two the B or the b allele. The alleles are copied down into the internal containers (see the internet internet site for a image), giving the genotype of the offspring. thus, the B of the mummy could combine with the two the B or the b of the daddy, and the comparable with the b allele. as a result, the possibilities for the offspring are BB (one out of four possibilities of being homozygous for the dominant trait and expressing it), Bb (2 out of four possibilities of being heterozygous for the trait, and expressing the dominant trait), or bb (one out of four possibilities of being homozygous for the recessive trait, and expressing it.

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