In humans, the COL1A1 locus codes for a collagen protein found in bone. A recess
ID: 37021 • Letter: I
Question
In humans, the COL1A1 locus codes for a collagen protein found in bone. A recessive COLA1 allele believed to reduce bone density and increase risk of fractures differs from the wildtype allele by the presence a G --> T in the first intron of the gene. This mutation can be easily screened by PCR, using COL1A1-specific primers followed restriction enzyme digest of the product with MscI. The normal allele is denoted as G and the recessive allele as T. A recent study of 894 women found that 570 were GG, 291 were GT and 33 were TT. (Assume for this exercise that these values reflect both male and female values for the sampled population.) (3
a. What are the frequencies of each allele?
b. What are the frequencies of each genotype?
c. Is this locus in Hardy-Weinberg equilibrium? Use the chi-square table below to evaluate the significance of any deviation from H-W expectations.
Explanation / Answer
b. The frequency of each genotype can be calculated as:
GG (p2) = 570/894 = .6375
GT (2pq) = 291/894 = .3255
TT (q2) = 33/894 = .0369
a. Allele frequencies can be calculated as:
Frequency of G = p = p2+1/2 (2pq)
= .6375 + 1/2 (.3255)
= .8002
Frequency of T = q = 1-p
= 1 - .8002
= .1998
c.To use the chi square table we need to calculate the expected genotype frequencies. Then we have to find the expected chi square value. After that we compare this value with the chi square table value. Since the table is not given the comparison cannot be done at the moment. But the result is based on the fact that when the calculated chi square is less than the chi suare of table with less difference then the population is in Hardy- Weinberg Equilibrium, while if the calculated value is more then the population is not in the Hardy- Weinberg Equlibrium.