Storr disease is inherited as an autosomal recessive in hobbits. In a certain ho

Question

Storr disease is inherited as an autosomal recessive in hobbits. In a certain hobbit population, the frequency of Storr disease is 1%.  

a) If the population is assumed to be in Hardy-Weinberg equilibrium with respect to Storr disease, what is the frequency of the allele that causes the disease?
b) What would be the frequency of heterozygotes?
c) What is the probability of two heterozygotes marrying?
d) In children of such matings, what would be the frequency of Storr disease?
e) What proportion of all Storr disease births are produced by heterozygous matings?

Explanation / Answer

Storr disease.................. is autosomal recessive (ss)

Frequency of storr disease is...................1%

ss = 1%

q2 = 1% = 0.01

q = square root of q2

q = square root of 0.01 = 0.1

since p = 1- 0.1 = 0.9

p+q =1

0.9+0.1 = 1

p2+2pq+q2 =1

(0.9)2 +2(0.9x0.1)+(0.1)2 = 0.81 + 0.18 +0.01 = 1

p2 = 0.81

q2 = 0.01

2pq = 2 x 0.9 x 0.1 = 0.18 = 18 % are heterozygotes

a). frequency of the allele which causes disease = q = 0.1 or 10%

b). frequency of heterozygotes = 0.18 or 18%

c). what is the probability of two heterozygotes marrying = Ss x Ss ..............

The ratio is .............1:2:1 or 3:1

The probability of normal is 3/4 to affected is 1/4

The probability of carrier is 2/4

The probability of affected is 1/4

d).frequency of Storr disease is 1%, that is 1 in 100

The marriage between two affected persons , the frequency of storr disease

1/100 x 1/100 = 0.0001 or 1 in 10,000

e. What proportion of all storr disease births are produced by heterozygous matings

18% is expected to be carriers in the population.

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