In humans, lack of fingernails is an exremely rare condition caused by a dominan
ID: 316138 • Letter: I
Question
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 0.10Explanation / Answer
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 mFMmFF
Myopia
No Fingernails
MmFf
Myopia
No Fingernails
mmFF
Normal vision
No Fingernails
mmFf
Normal vision
No Fingernails
mfMmFf
Myopia
No Fingernails
Mmff
Myopia
Fingernails present
mmFf
Normal vision
No Fingernails
mmff
Normal vision
Fingernails present
mFMmFF
Myopia
No Fingernails
MmFf
Myopia
No Fingernails
mmFF
Normal vision
No Fingernails
mmFf
Normal vision
No Fingernails
mfMmFf
Myopia
No Fingernails
Mmff
Myopia
Fingernails present
mmFf
Normal vision
No Fingernails
mmff
Normal vision
Fingernails present