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How to construct pedigree?

In humans, the ability to taste a chemical called PTC — a taster, is correlated with a dominant allele, T, whereas the inability to taste this substance — non-taster, is correlated with the recessive allele t. Additionally, the allele for brown eyes B, is dominant over the allele of blue eyes, b. Jerry, who is a taster with brown eyes, marries Jane, who is a taster with blue eyes. They have a daughter, Jerrijane, who is a non-taster with brown eyes, and a son, Jerry Jr., who is a taster with blue eyes. Jerry Jr. marries, and has three children. Two of his children are tasters with brown eyes, and the other is a non-taster with brown eyes.

(a) Construct the pedigree for this family.

(b) What is Jerry’s genotype?

(c) What is Jane’s genotype?

(d) What is Jerrijane’s genotype?

(f) What is Jerry Jr.’s genotype?

(f) What is/are the possible genotype/s of Jerry Jr.’s wife?

(d) What are the expected ratios of the possible genotypes of this cross?

(e) What are the expected ratios of the possible phenotypes of this cross?

My teacher did not cover pedigree in our class but we are still responsible for the material. google is only getting me so far, i am so confused..

1 Answer

  • 8 years ago
    Favorite Answer

    Lots of questions here. :-)) I'm going to point you to a website that shows you how to construct a pedigree for traits like this:

    After you do that, you can use the pedigree to draw conclusions from your data about what everybody's genotypes are.

    (b) Since Jerry is a taster, he is either TT or Tt in that locus. However, since JeriJane (Jerry's daughter) is a nontaster, and nontaster is recessive, she MUST have inherited the recessive allele (t) from Jerry. Therefore Jerry can't be TT, meaning he is Tt in the taster locus. Next, since Jerry has brown eyes, he can be either BB or Bb in that locus. Again, we have to look at his children, specifically Jerry Jr. Jerry Jr has blue eyes, which means his genotype is bb in the eye-color locus. That means he inherited one recessive allele (b) from his mom and one from his dad. Therefore, Jerry must have a recessive allele for eye color to pass down (b). Jerry's genotype: TtBb.

    (c) Jane is a taster, but since Jerijane is a nontaster, Jane is heterozygous (Tt) in this locus. Jane is blue eyed, so she is bb in the eye color locus. Jane's genotype: Ttbb.

    (d) Jerrijane ... Nontaster, so tt there. Brown eyes, which would mean either BB or Bb, but Jane has no dominant allele to give her. Since children inherit one allele from dad (B in this case) and one from mom (must be a b, since that's the only kind of eye color allele that Jane has), Jerijane is Bb in the eye color gene. Ultimate genotype: ttBb.

    It's not as exhausting as it looks, really. You just have to use a little reasoning.

    (e) Jerry Jr ... Taster, so could be either Tt or TT. More on this later. In the eye color locus, he must be bb, since he has a phenotype of blue eyes.

    Here's the LATER: It says one of Jerry Jr's kids is a nontaster. The genotype of a nontaster is tt, which definitely means Jerry Jr passed down a recessive allele (t). Therefore, even though I said it was possible that Jerry Jr could be either Tt or TT, that's not true. The only way he could have a kid who is a nontaster is if he has a recessive allele (t) to pass down. So Jerry Jr can't be homozygous dominant in the taster locus. Jerry Jr's ultimate genotype is Ttbb.

    Jerry Jr's wife (we're using too many possessive's here;) must have brown eyes, because Jerry Jr has no B alleles to give and they have a history of having brown-eyed children (if even one has brown eyes, you KNOW the wife has brown eyes). It's possible for her to be BB or Bb (you can't tell from the info given), but her phenotype is for sure brown eyes.

    As for Jerry Jr's wife's genotype in the taster locus, we know Jerry Jr is Tt in this locus and we are told they have both taster and nontaster kids. Therefore we don't know Jerry Jr's wife's phenotype for taster, but we can eliminate the possibility that she is TT at this locus. The only way she could have even one kid who was a nontaster is if she had a recessive allele (t) to give. So, her possible phenotypes are taster-brown and nontaster-brown; possible genotypes are TtBB, ttBB, TtBb or ttBb.

    If you need help with the Punnett squares for the last two parts of your question, just ask. It's telling me I have 595 misspellings, so I'm getting a little worried.

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