Question

In humans, being a tongue roller (R) is dominant over non-roller (r). A man who is a non-roller marries a woman who is heterozygous for tongue rolling.

Father’s phenotype _______ Father’s genotype ______
Mother’s phenotype ________ Mother’s genotype _______

What is the probability of this couple having a child who is a tongue roller? Show your answers by drawing a Punnett’s square.

Answer 1

Answer:

Father’s phenotype non roller Father’s genotype rr

Mother’s phenotype roller Mother’s genotype Rr

Probability of this couple having a child who is a tongue roller : 1/2

Explanation:

Given that allele for rolling (R) is dominant over allele for non rolling (r).

Since father is a non roller his genotype would be rr

Mother is a heterozygous tongue roller so her genotype would be Rr

Their progeny:

Rr  X   rr  :

   R     r

r  Rr   rr

r  Rr   rr

Half of the offspring have Rr genotype which will make them tongue roller so probability of this couple having a child who is a tongue roller is 1/2.

Answer 2

The father’s phenotype is non-roller (genotype rr), whereas the mother’s phenotype is roller (genotype Rr).

What is a dominant allele?

A dominant allele is a gene variant capable of masking the recessive allele in heterozygous individuals.

• In this case, the father is recessive homo-zygous, whereas the mother is heterozygous, thereby the expected offspring proportion is 50% tongue roller (Rr) and 50% non-roller (rr).

• The Punnett square here is:

           R               r

r     1/4 Rr         1/4 rr

r     1/4 Rr         1/4 rr

In conclusion, the father’s phenotype is non-roller (genotype rr), whereas the mother’s phenotype is roller (genotype Rr).

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