a) The table above represents survivability information for two portions of the
ID: 3254243 • Letter: A
Question
a) The table above represents survivability information for two portions of the Lesser Snozzlewhompin life cycle. Using these values, calculate the survivability (), relative fitness (W) and partial generation selection coefficients of each genotype for the following periods: birth to weaning and weaning to mating.
b) How do the values you calculated in 3a differ between these two phases of the Lesser Snozzlewhompin life cycle? Which genotype is being selected against in each phase? What do the values you calculated suggest about the heterozygote genotype in the birth to weaning period?
c) Now that you have become a world expert on Lesser Snozzlewhompin population dynamics, the Global Lesser Snozzlewhompin Conservation Alliance asks you to analyze some long-term data that has been collected regarding the status of these animals in their native range. The data below represents the frequency of brown and white individuals observed at mating festivals over a 50-year period. Using these data, calculate the selection coefficient against the c allele over this time period. [Note: The data collection teams were unable to distinguish between the two genotypes producing brown coat color].
Phenotype Genotype born surviving to weaning making it to mating festival Brown Coat CC Cc 50 20 40 18 36 16 White Coat CC 25 20 10Explanation / Answer
Solution:
Survival rate = the overall survival rate is the % of individuals born that survive to reproductive age. But often we can only measure the % that survive over some period of time, e.g. the survival rate of fledglings, the survival rate from one year to the next, or the survival rate through a winter storm.
Reproductive rate = for any given genotype or phenotype, the average number offspring born per individual.
Relative Fitness (w) is the survival and/or reproductive rate of a genotype (or phenotype) relative to the maximum survival and/or reproductive rate of other genotypes in the population.
a) survivability from birth to weaning:
CC- 40 out of 50
Cc-18 out of 20
cc-20 out of 25
relative fitness with respect to CC:
CC=40/40=1
Cc=18/40= 9/20
cc= 20/40=1/2
Selection Coefficients:
relative fitness = 1 + s; s is the selection coefficient
For CC: s= 1-1=0
Cc=9/20-1=-0.55
cc=1/2-1=-0.5
relative fitness with respect to Cc:
CC=40/18=20/9
Cc=1
cc=20/18=10/9
Selection Coefficients:
relative fitness = 1 + s; s is the selection coefficient
For CC: s= 2.22-1=1.22
Cc=1-1=0
cc=10/9-1=0.11
relative fitness with respect to cc:
CC=40/20=2
Cc=18/20=9/10
cc=1
Selection Coefficients:
relative fitness = 1 + s; s is the selection coefficient
For CC: s= 2-1=1
Cc=9/10-1=-0.1
cc=1-1=0
survivability from weaning to mating:
CC- 36 out of 40
Cc-16 out of 18
cc-10 out of 20
relative fitness with respect to CC:
CC=1
Cc=16/36= 4/9
cc= 10/36=5/18
Selection Coefficients:
relative fitness = 1 + s; s is the selection coefficient
For CC: s= 1-1=0
Cc=4/9-1=-0.55
cc=5/18-1=-0.72
relative fitness with respect to Cc:
CC=36/16=9/4
Cc=1
cc=10/16=5/8
Selection Coefficients:
relative fitness = 1 + s; s is the selection coefficient
For CC: s= 9/4-1=1.25
Cc=1-1=0
cc=5/8-1=-0.375
relative fitness with respect to cc:
CC=40/10=4
Cc=18/10=9/5
cc=1
Selection Coefficients:
relative fitness = 1 + s; s is the selection coefficient
For CC: s= 4-1=3
Cc=9/5-1=0.8
cc=1-1=0
b)Absolute fitness is the number of offspring contributed to the next generation. Knowing this number for a genotype does not tell us whether that genotype is doing poorly or well, unless we know the fitness of other genotypes. Relative fitness shows how much fitness an allele or genotype has compared to the maximum fitness, and so whether it will increase or decrease.
The most direct way is to mate a heterozygous male fruit fly to a female of known homozygous genotype. You will then be able to determine the number of each genotype of offspring, which will give you the relative fitness of each allele.
So, it is clear that the selection coefficient for birth to weaning is higher than the weaning to mating.
The heterozygote genotype in the birth to weaning period is considered to be the best for mating purpose as the selection coefficient is much higher than other genotypes.
c) Reducing the heterozygous effect reduces the frequency p of C at which the increase of C is greatest, while increasing the effect increases this frequency. We can make sense of this in the following terms. When the heterozygous effect is increased, and the fitness of heterozygotes becomes as low as that of the cc homozygotes, selection at higher frequencies of C becomes relatively more effective, compared to selection at low frequencies of C, because in the first case it mostly operates with the heterozygotes in the population.
Genotype (CC & Cc):
p(t) = p(0)WCt/ p(0)WCt+ q(0)Wct
Wc = 1 + s;
p(t)=0.84
WC=1
WCt=1t
t=50
WCt=1
p(0)=0.54
q(0)=1-0.54=0.44
Wc=0.3068
s=1-Wc
selection coefficient,s=0.6932
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