Question

In mice, fur color is a genetically determined trait. To observe the effects of natural selection on fur color in mice, scientists set up six enclosures with either light- or dark-colored sand on the ground. The enclosures were isolated from all ground predators and wild mice but accessible to predatory birds. The scientists placed equal numbers of light- and dark-colored mice into each enclosure. A total of 500 mice were used in the experiment. After several generations, the scientists sampled the mice and found that populations in the light sand enclosures were, on average, lighter in color than the original population, while those in the dark sand enclosures were, on average, darker in color than the mice in the original population.
a) describe the way the scientists will determine the evolutionary fitness of the mice in the experiment.


b) Identify the independent variable in the scientists’ experiment.


c) State the null hypothesis


d) The scientists claim that the changes in the frequency of fur color were the result of natural selection. Justify their prediction.

Answer 1

Answer/Explanation:

A. Evolutionary fitness simply refers to the ability of a species of organism to reproduce and survive, thereby leaving more of its offspring with its genes to contribute, relatively, largely to the gene pool in the next generation.

The scientist can determine the evolutionary fitness of the mice in the experiment by calculating the relative fitness of each genotype found in the mice. I.e. each genotype survival and/or reproduction rate ÷ highest survival and/or reproduction rate among the genotypes inherent in the mice population. Or simply, instead of calculating the relative fitness of each genotype, the scientist can simply calculate the relative fitness of each phenotype found in the mice.

B. The independent variable used by the scientist is the variable that is being manipulated here or changed, to see what effect it has on the dependent variable. The varied environment is the independent variable upon which fur color is dependent on.

C. Null hypothesis could be:

Natural selection has no effect on fur color of mice

Or

There is no effect of varied environment on fur color of mice.

D. Change of Allele frequencies for fur color as can be seen from the experiment, is mostly determined here by natural selection. What occured here is a type of selection called diversifying selection. The ability of the mice to blend together with the background of their environment makes each mice at both spectrum or extreme to be selected and favoured over intermediate individuals. Those individuals who cannot blend are being preyed upon by predatory bird, thereby reducing the number of individuals who are neither of the two extreme colors.

The claim of the scientist is justified, as the frequency of fur color would change overtime as a result of natural selection that occured.

Answer 2

The correct answers to these questions are the following:

1) By analyzing enclosures with different colors on the ground that can either favour or hinder the success of the populations.

2) Independent variable: number of generations.

3) Null hypothesis: different colors have no effect on the fitness of the populations.

4) It is a consequence of directional selection. Directional selection is a type of natural selection where the frequency of a trait is modified to benefit a phenotype in response to a change in the environmental conditions.