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Homework answers / question archive / Myotonic dystrophy is an autosomal recessive disorder affecting 1 in 500 people in Quebec
Myotonic dystrophy is an autosomal recessive disorder affecting 1 in 500 people in Quebec.
a. What is the expected frequency for the dominant allele in the Quebec population?
b.What is the expected frequency for the recessive allele in the Quebec population?
c.What percent of the Quebec population would you expect to be homozygous for the normal (non-disease) allele?
d. Myotonic dystrophy affects one in 7500 people in all of Canada. What would be the expected frequency of carriers of myotonic dystrophy in Canada?
e.Assuming the population of Canada is 30 million people, what number of people in Canada would you expect to be carriers?
Answer:
(a) 0.9552
(b) 0.04472
(c) 99.99%
(d) 2.283 %
(e) 684820 people
Step-by-step explanation
Lets apply Hardy-Weinberg equations;
p2 + 2pq + q2 = 1
p + q = 1
Whereby;
p = frequency of the dominant allele
q = frequency of the recessive allele
p2 = % of homozygous dominant individual in the population
2pq = % of heterozygous individual in the population
q2 = % of homozygous recessive individual
(a)
% of homozygous recessive individual = 1/500 x 100 = 0.2 % or 0.002 hence;
q2 = 0.002
q = (0.002)^1/2 =0.04472
p + q = 1
p = 1 - q
p = 1 - 0.04472 =0.9552
The frequency of the homozygous dominant allele = 0.9552
(c)
frequency of homozygous recessive allele = q =0.04472
(d)
% of homozygous normal for the allele = p2
p =0.9552
p2 = (0.9552)^2 = 0.9999 or
p2 = 0.9999 x 100% = 99.99%
(d)
q2 = 1/7500 x 100 = 0.013333 % or 0.00013333
q = (q2)^1/2
q = (0.000133333)^1/2 = 0.011547
p + q = 1
p = 1 - q
p = 1 - 0.011547
p = 0.98845
% of heterozygous individuals/carriers = 2pq
2pq = 2(0.98845 x 0.011547) = 0.022827
2pq = 0.022827 x 100 % = 2.283 %
(e)
Number of expected to carriers = percentage of carriers/100 x 30 million
Number of expected to carriers = 2.283/100 x 30000000
Number of people expected to be carries = 684820 people
