In humans lack of fingernails is an exremely rare condition

In humans, lack of fingernails is an exremely rare condition caused by a dominant allele. Myopia (near-sighted) is a common condition also caused by a dominant allele. A woman, whose mother had normal vision and fingernails, is myopic and has no fingernails. Her husband has normal vision and has no fingernails. They plan to have 6 children. What is the probability that one will have no fingernails, but normal vision, one will have no fingernails and myopia, and the rest will have neither condition?

0.001 0.01 O 0.06 O 0.10

Solution

Here, a very important point is that both Myopia and lack of fingernails is caused by a dominant allele. To express a dominant character in a phenotype only one allele is required.

Given that,

1. Mother - Normal Vision and Fingernails

2. Daughter (Myopic + No Fingernails)

3. Husband (Normal vision + No Fingernails)

Let M be the dominant allele for Myopic condition.

Let m be the recessive allele for Normal vision condition.

Let F be the dominant allele for Lack of Fingernails condition.

Let f be the recessive allele for having Fingernails condition.

Woman genotype is Mm for Myopia and Ff for lack of fingernails. Here woman is heterozygous for both the traits because the mother is with normal vision (mm) and fingernails (ff).

Woman\'s husband genotype is mm for normal vision and Ff for lack of fingernails. We assume that the husband is heterozygous for lack of fingernails here.

Possible gametes from woman and husband are as follows

To solve for a dihybrid cross, we need to deduce the gametes of both woman and husband.

F1 MmFf x mmFf

Woman vs Husband

MmFF

Myopia

No Fingernails

MmFf

Myopia

No Fingernails

mmFF

Normal vision

No Fingernails

mmFf

Normal vision

No Fingernails

MmFf

Myopia

No Fingernails

Mmff

Myopia

Fingernails present

mmFf

Normal vision

No Fingernails

mmff

Normal vision

Fingernails present

MmFF

Myopia

No Fingernails

MmFf

Myopia

No Fingernails

mmFF

Normal vision

No Fingernails

mmFf

Normal vision

No Fingernails

MmFf

Myopia

No Fingernails

Mmff

Myopia

Fingernails present

mmFf

Normal vision

No Fingernails

mmff

Normal vision

Fingernails present

Probability of getting no fingernails but normal vision is 6/16

No fingernails and myopia is 6/16

Normal vision and fingernails present 2/16

To determine the given condition, we multiply the independent events

6/16 X 6/16 X 2/16 = 0.017

Hence 0.01 is the correct answer.

F2	MF	Mf	mF	mf
mF	MmFF Myopia No Fingernails	MmFf Myopia No Fingernails	mmFF Normal vision No Fingernails	mmFf Normal vision No Fingernails
mf	MmFf Myopia No Fingernails	Mmff Myopia Fingernails present	mmFf Normal vision No Fingernails	mmff Normal vision Fingernails present
mF	MmFF Myopia No Fingernails	MmFf Myopia No Fingernails	mmFF Normal vision No Fingernails	mmFf Normal vision No Fingernails
mf	MmFf Myopia No Fingernails	Mmff Myopia Fingernails present	mmFf Normal vision No Fingernails	mmff Normal vision Fingernails present