You have a population of cockroaches in your kitchen that amounts to 500 adult i

Question

You have a population of cockroaches in your kitchen that amounts to 500 adult individuals. You are tired of living with these scavengers, so you decide to go to the hardware store and buy an insecticide to murder the little devils. You thoroughly spray your kitchen and you are satisfied with the result. Please do some simple calculations below to determine whether your satisfaction is warranted.

1.Remember, you’re starting with 500 individuals. Let’s assume that your kill rate was 98% effective. How many roaches were killed by your treatment?

500 x 0.98 = __490_____ (number killed)

Individuals remaining = _____10_____  

You pick up your trusty can of Raid and spray again and again just to make sure.    And yet this time, the result is very different. We’re going to assume again that you have a population of 500 roaches in your kitchen. But this time, the kill rate is 10%. OMG!!

3.How did this happen? Write a paragraph explaining how this second result is possible.

a.500 x 0.10 = __50______ (number killed)

b.Individuals remaining = ___450________

Recall that as diploid organisms, we have two copies of every gene—one from your mother and one from your father. It is also the case that MOST genes for resistance are recessive. This means that the gene for susceptibility is dominant and that a resistant organism would have to have two copies of the gene for resistance to show the trait. With these simple ideas in mind, do some more calculations—

4.In the original population (described in (A) above, before insecticide treatment), calculate the total number of genes for the pesticide trait in the population. I will calculate the first one. You do the rest.

Number of individuals 500 x Number of copies of gene per individual 2 = 1000 genes for trait

Now, remember that some of the individuals in A. are susceptible and some are resistant

a.Multiply the total number of genes for the pesticide trait by the proportion of susceptible individuals to get the total number of susceptible genes in the population   _10000_________ (Hint: you determined this in part A. Second Hint: you can assume that all individuals are homozygous, i.e., that they have only one allele---either the susceptible one or the resistant one).

b.Multiply the total number of genes for the pesticide trait by the proportion of resistant individuals (or determine by subtraction) to get the total number of resistant genes in the population__100000_________

c.What is the percent of both forms of the gene in the initial population? ________

5.Now, do the same calculations for the second population, that was generated after you sprayed for the roaches the first time.

Number of susceptible genes in population_50000__________

Number of resistant genes in population___450000_________  

Percent of resistant genes in population___________  

Please answer these questions about the results of question 5.

6.Does this result meet the definition of evolution? Explain using the numbers you generated in Questions 1 and 2.

7.Assuming that the trend established continues with subsequent sprays, what can you expect to happen in your kitchen if you continue the same treatment regime? Explain.

8.Should you move?

Explanation / Answer

Answer to Question 3.

Assuming that the gene of susceptibility is dominant over resistance gene which is recessive and the 500 individuals are homozygous. The first time the spray was done, encounter of the organism with the chemical was for the first time, so the individuals who are homozygous resistant or are the fittest, survives the chemical's toxicity, while the rest died. These survived individual, cope with the chemical's effect and simultaneously the body build up resistance for the same. This development of resistance brings about genetic change in the individual. However when the population was again 500 and again the same chemical was sprayed, most of the survived, because these ornganisms are the progeny of the individuals with acquired resistance or the ones with resistant gene. Since most of the roaches with susceptible gene are dead in the first round of spray, so the population present now are mostly the ones who carries copies of allele of resistance only, hence the effect of pesticide was drastically less than that of the first time. the ones who died in the nd round of pesticide spray, were the ones with acquired resistance, which can be reversible and make the roaches susceptible to pesticide; while most population survived the pesticide.

answer 4 (with respect to population one...)

a) There are 1000 genes of trait for pesticide, proportion of susceptible population to overall population is 490/500. thus the total number of susceptible gene = (490/500)*1000 = 980 genes; and

b) Proportion of resistance population to overall population is 10/500. thus the total number of resistant gene = (10/500)*1000 = 20 genes.

c) The percentage of susceptible genes = (980/1000)*100 = 98%.

  The percentage of susceptible genes = (20/1000)*100 = 2%.

5. a) There are 1000 genes of trait for pesticide, proportion of susceptible population to overall population is 50/500. thus the total number of susceptible gene = (50/500)*1000 = 100 genes; and

b) Proportion of resistance population to overall population is 450/500. thus the total number of resistant gene = (450/500)*1000 = 900 genes.

c) The percentage of susceptible genes = (100/1000)*100 = 10%.

  The percentage of susceptible genes = (900/1000)*100 = 90%.

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