Question

In: Biology

The ability to taste the chemical, phenylthiocarbamide (PTC), is determined by a gene on chromosome 7...

  1. The ability to taste the chemical, phenylthiocarbamide (PTC), is determined by a gene on chromosome 7 that shows dominant inheritance. PTC-like chemicals are found in vegetables like broccoli and cabbage. Tasters don’t enjoy eating these types of vegetables while non-tasters don’t notice this bitter taste in these vegetables. (T= ability to taste PTC; t= non-taster) Determine the probability that the following couples (a, b, and c) will have a non-taster child. Support your answer with a Punnett square.
    1. Two tasters, who are both heterozygous:
    1. A non-taster marries a taster who is homozygous:
    2. Two non-tasters:
    3. Can a non-taster have 2 biological parents that are both tasters?

Solutions

Expert Solution

**Alleles of the trait tasting are

T - ability to taste PTC (dominant allele)

t - non-taster (recessive allele)

**Genotypes and phenotypes are

  • TT - Taster
  • Tt - Taster
  • tt - Non taster

a) Punnet square

Both parents are tasters who are heterozygous

Both have genotype Tt

Possible genotypes of offsprings are TT,Tt and tt

1 out of 4 children has genotype tt and they are non tasters

Probability of having non-taster child = 1/4 = 25%

b) Punnet square

One parent - non-taster (genotype - tt)

One parent - homozygous taster (genotype - TT)

Possible genotypes of offsprings is Tt only who will be taster.

Probability of having non-taster child = 0%

c)Punnet square

Both parents are non-tasters who have genotype tt

Possible genotype of offsprings is tt only. So all children will be non-tasters.

Probability of having non-taster child = 100%

d) Yes. A non-taster can have 2 biological parents that are both tasters.

This is possible when both parents are heterozygous Tt (tasters)

Then there is 25% chance of having non-taster children.

This scenario is same as question (a)


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