Question

Your task is to solve the following problems. For each, you must provide a written response and a supporting Punnett square. Your Punnett square must be drawn by hand.

The ability to roll the tongue sideways (A) is dominant over the inability to roll one's tongue (a). In humans, non-attached earlobes (B) are dominant over attached earlobes (b). Two parents with attached earlobes can roll their tongues. They are both heterozygous for the tongue rolling trait.

1. What is the genotype of the mother?
2. What is the genotype of the father?
3. Whare are the possible gametes from the mother?
4. What are the possible gametes from the father?
5. Draw the Punnett square, and combine the gametes to produce offspring.
6. What is the phenotypic ratio of these offspring?

Answer 1

It is given that the ability to roll the tongue sideways (A) is dominant over the inability to roll one's tongue (a) and non-attached earlobes (B) are dominant over attached earlobes (b).

Both the parents have attached earlobes and they can roll their tongue.

Genotype of the mother will be bbAa (given that she is heterozygous for tongue rolling trait)

Genotype of the father will be bbAa (given that he is heterozygous for tongue rolling trait)

Note:Attached ear lobe is possible only if both the alleles are recessive i.e.,bb

Gametes from the mother are bA,bA,ba and ba.

Gametes from the father are bA,bA,ba and ba.

Punnet square to find out F1 progenies

	bA	bA	ba	ba
bA	bbAA	bbAA	bbAa	bbAa
bA	bbAA	bbAA	bbAa	bbAa
ba	bbAa	bbAa	bbaa	bbaa
ba	bbAa	bbAa	bbaa	bbaa

bbAA-attached earlobe and can roll the tongue (4 out of 16 progenies)

bbAa-attached earlobe and can roll the tongue (8 out of 16 progenies)

bbaa-attached ear lobe and can not roll the tongue (4 out of 16 progenies)

Phenotypic ratio will be, attached earlobe with tongue rolling ability:attached earlobe without tongue rolling ability=12:4

=3:1

Genotypic ratio will be, bbAA:bbAa:bbaa=4:8:4

=1:2:1