. A population in Chile that lives in a harsh desert environment had an outbreak
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Question
. A population in Chile that lives in a harsh desert environment had an outbreak of cholera during the summer that killed many people. This population was tested for the presence of CFTR alleles. The numbers of each genotype in the population before and after the outbreak are shown below.
+ / + + / F508 F508 / F508 Total
Spring 1575 540 85 2200
Fall 660 540 0 1200
What is the fitness of each genotype?
What is the allele frequency in the population in the fall after the cholera outbreak? P c.Assuming no further occur, what will be the allele frequencies in the next generation?
d. What will be the genotype frequencies in the next generation
e. Provide a biochemical, cellular, or molecular hypothesis as to why the three different genotypes should have different fitness.
Explanation / Answer
The fitness of each genotype is calculated as follows:
Genotype
+/+
+/F508
F508/ F508
Total
Spring
1575
540
85
2200
Fall
660
540
0
1200
Survival rate
42% or 0.42
100 % or 1
1.2 % or 0.01
Survival rate is calculated by dividing the surviving fraction with total number or individuals (multiplied by hundred for percentage)
Fitness is the survival rate of a genotype divided by the highest survival rate among the three genotypes. The highest survival rate is 100%. (assuming that there is no reproduction)
Relative survival rates are 0.42, 1 and 0.01 for the given genotypes respectively
Allele frequency:
f(p), that is (+) = 1320 + 540/2400 = 0.775
f(q) that is (deltaF508) = 540/2400 = 0.225
d. Allele frequency in next generation:
Approximately, 80% of gametes are +
Approximately, 20% of gametes are F508
The probability of A sperm meeting an A egg is 0.8 0.8 = 0.64
The probability of A sperm meeting and a egg is 0.8 0.2 = 0.16
The probability of a sperm meeting an A egg is 0.2 0.8 = 0.16
The probability of an a sperm meeting an a egg is 0.2
Thus, the probability of +/+ offspring is 0.64, +/ F508 is 0.32 and F508/ F508 is 0.04
e. CFTR gene is involved in transportation of chloride ions across the membranes. The F508 heterozygous individuals have a certain degree of resistance towards cholera as the mutant gene is resistant to transportation of ions. Majority of homozygous normal individuals are prone to cholera and most of the homozygous F508 individuals didnot survive due to cystic fibrosis.
Genotype
+/+
+/F508
F508/ F508
Total
Spring
1575
540
85
2200
Fall
660
540
0
1200
Survival rate
42% or 0.42
100 % or 1
1.2 % or 0.01
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