certain I don\'t know how to do this problem can someone help? A certain recessi
ID: 180198 • Letter: C
Question
certain I don't know how to do this problem can someone help?
A certain recessive gene (r) in a population has frequency of 0.5. As a result of movement of the population to a new environment, homozygous recessive individuals (rr) are now selected against, with a loss of 80% of the homozygotes before maturity. Homozygous dominant (RR) and heterozygotes (Rr) are not affected. Assuming the population starts our in HW equilibrium.
a. What is the selection coefficient against r?
b. What are the relative fitnesses of the 3 genotypes?
c. What are the genotype and allele frequencies in the population after one generation of selection ?
Explanation / Answer
If they are in HW equilibrium:
R = p
r= q
To find out the expected frequency of the homozygotes or the heterozygotes, we need to find the allelic frequency of both p and q.
Here, the allelic frequency of 'r' is given to be as 0.5
Therefore, the expected frequency of the genotype rr according to the HW law would be :
rr = 0.5 (allelic frequency)
genotypic frequency : q2 * 1000
= [(0.5)2 * 1000]
=250
2) Since the survival rate of the recessive homozygotes are 20% (Loss of 80%), reproductive rate is assumed to be equal for all three genotypes, and the highest survival rate is taken to be 100% (unless otherwise mentioned), the relative fitness are
rr Rr RR Highest Survival
survival rate 20 100 100 100
Relative Fitness(w) (20/100)= 0.2 (100/100) = 1 (100/100)= 1
1) Selection coefficient against r
Selection coefficient = 1-W
= 1-0.2
=0.8
3) Genotype frequency and allele frequency for r = ( 20% of 250) as determined from the first generation
= 50
Genotpye frequency is 50
Allele frequency = square root of 50/1000
= 0.2236
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