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

The scientists can assess evolutionary fitness by tracking the reproductive success of mice, with the color of the sand as the independent variable and the null hypothesis being that sand color has no effect on fur color distribution. Changes in fur color frequencies are justified as a result of natural selection due to selective predation pressures, leading to an increase in the frequency of fur color that offers better camouflage in the given environment.

Step-by-step explanation:

In an experiment to observe evolutionary fitness and natural selection on fur color in mice, scientists could determine the evolutionary fitness of a population by evaluating which coloration confers a survival advantage that results in greater reproductive success in the given environment. This could be done by counting the offspring of light and dark-colored mice in each enclosure over several generations.

The independent variable in the scientists’ experiment is the color of the sand in the enclosures, which corresponds to the environment in which the mice populations live. This environmental factor would influence the natural selection process as the mice with fur color that blends in more effectively with the sand color would likely have a higher survival rate from predation.

The null hypothesis for this experiment would be that the color of the sand has no effect on the fur color distribution in the mouse populations after several generations. This null hypothesis assumes that the frequencies of light and dark fur coloration in the mice populations will remain unchanged despite the differences in sand color in their respective enclosures.

Justifying the prediction that changes in the frequency of fur color are the result of natural selection, one could argue that since the enclosures are exposed to predatory birds, mice that match the sand color are less likely to be seen and eaten by these predators. Over time, this selection pressure would result in an increase in the frequency of fur color that best camouflages with the environment. This is similar to the known case of the peppered moth and other examples where population genetics shift towards more successful phenotypes due to selection pressures.

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.