Question

Suppose "A" is a dominant gene for the ability to taste phenylthiocarbamide and "a" is a recessive gene for the inability to taste it. Which couples could possibly have both a child who tastes it and a child who does not?​

Answer 1

Complete question:

Suppose "A" is a dominant gene for the ability to taste phenylthiocarbamide and "a" is a recessive gene for the inability to taste it. Which couples could possibly have both a child who tastes it and a child who does not?​

a. father AA, mother aa

b. father Aa, mother AA

c. father Aa, mother Aa

d. father AA, mother AA

Answer:

c. father Aa, mother Aa

Explanation:

According to the given information, the ability to taste phenylthiocarbamide is a dominant trait and is imparted by the allele "A". This phenotype would be expressed in both homozygous and heterozygous conditions. The non-taster phenotype would be expressed in the homozygous recessive genotypes only.  

To have both taster and non-taster children, both the parents should have at least one copy of the recessive allele. Among the given options, the father with genotype Aa and the mother with genotype Aa have the possibility to have both taster and non-taster children.

Aa x Aa= 3/4 taster (1/4 AA and 1/2 Aa): 1/4 non-taster (1/4 aa)

Answer 2

Assuming complete dominance, in which the dominant allele hides the expression of the recessive allele, the correct option is C. father Aa, mother Aa.

What is complete dominance?

Complete dominance occurs when one of the alleles of a gene completely masks the expression of the other allele. The first one is the dominant allele and the hidden one is the recessive allele.

Individuals that are heter0zyg0us for a particular gene, only express the dominant trait although they are carrying the recessive allele. The dominant allele is hiding the expression of the recessive allele.

In the exposed example, we will assume that the trait is coded by a single diallelic gene that expresses complete dominance.

• A is the dominant allele and codes for the ability to taste phenylthiocarbamide

• a is the recessive allele and codes for for the inability to taste it

Possible crosses:

a. father AA, mother aa

b. father Aa, mother AA

c. father Aa, mother Aa

d. father AA, mother AA

The only possible couple that could produce both a child who tastes phenylthiocarbamide and a child who does not is if both parents are heter0zyg0us for the trait.

Cross: between heter0zyg0us individuals

Parentals)  Aa    x    Aa

Gametes)   A   a    A    a

Punnett square)    A      a

                    A     AA    Aa

                     a    Aa     aa

F1) Genotype

1/4 = 25% of the progeny is expected to be h0m0zyg0us dominant, AA

2/4 = 50% of the progeny is expected to be heter0zyg0us, Aa

1/4 = 25% of the progeny is expected to be h0m0zyg0us recessive, aa

    Phenotype

3/4 = 75% of the progeny is expected to taste phenylthiocarbamide

1/4 = 25% of the progeny is expected not to taste phenylthiocarbamide

The correct option is C. father Aa, mother Aa

a. father AA x  mother aa  ⇒ F1) 100% Aa

b. father Aa, mother AA ⇒ F1) 50% AA and 50% Aa

c. father Aa, mother Aa ⇒ F1) 25% AA, 25% aa, 50% Aa

d. father AA, mother AA ⇒ F1) 100% AA

You will learn more about complete dominance at

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