a) Describe one measure of evolutionary fitness.
(c) Based on the data, identify the population that is likely to have the highest frequency of heterozygotes. Assuming random mating, calculate the frequency of animals in population 1 that carry both alleles 1 and 3.
d) A sudden event drastically changes the habitat of each population such that most of the normal vegetation and insects are replaced by other vegetation and insects. One of the scientists claims that population 2 will be the most severely affected. Predict the most likely effect of the event on population 2. Provide reasoning to justify your prediction.
The Correct Answer and Explanation is:
a) Describe one measure of evolutionary fitness.
Correct Answer:
One common measure of evolutionary fitness is reproductive success, defined as the number of viable offspring an individual contributes to the next generation relative to other individuals in the population.
Explanation:
Evolutionary fitness, often referred to as Darwinian fitness, measures an organism’s success in passing its genes to the next generation. It is not simply about survival, but about reproductive output. An organism that lives a long life but produces no offspring has zero fitness. In contrast, an organism that produces many offspring that themselves reproduce has high fitness. Fitness can be quantified by calculating the relative contribution of an individual’s genotype to the gene pool of the next generation. In populations where certain alleles confer advantages in survival or reproduction, individuals with those alleles tend to leave more offspring. Over time, this leads to an increase in the frequency of those alleles in the population, a process known as natural selection.
(c) Identify the population with the highest frequency of heterozygotes. Calculate frequency of animals in population 1 that carry both alleles 1 and 3.
Correct Answer:
Assuming random mating and Hardy-Weinberg equilibrium, the population with the highest allelic diversity (i.e., more evenly distributed allele frequencies) is likely to have the highest frequency of heterozygotes.
To calculate the frequency of animals carrying both alleles 1 and 3 in population 1:
Let:
- Frequency of allele 1 = p
- Frequency of allele 3 = q
Then the heterozygote frequency for genotype 1/3 = 2pq
Example Calculation (Assuming p = 0.4, q = 0.3):
2pq = 2 × 0.4 × 0.3 = 0.24 or 24%
Explanation:
In population genetics, heterozygosity is maximized when allele frequencies are equal. For a gene with multiple alleles, the highest heterozygosity occurs when allele frequencies are close to each other. The Hardy-Weinberg principle provides a framework for calculating genotype frequencies. The frequency of heterozygotes carrying two specific alleles, say allele 1 and allele 3, is calculated as 2pq, where p and q are the allele frequencies. If population 1 has intermediate frequencies for alleles 1 and 3, a substantial proportion of individuals will be 1/3 heterozygotes.
d) Predict the effect of environmental change on population 2. Justify your prediction.
Correct Answer:
Population 2 is likely to be the most severely affected because it has lower genetic diversity, making it less adaptable to sudden environmental changes.
Explanation
Populations with low genetic diversity are more vulnerable to environmental changes because they have a limited range of genetic traits to draw upon when adapting to new conditions. If population 2 has a high frequency of one or two dominant alleles and few rare alleles, its evolutionary flexibility is constrained. In contrast, populations with greater genetic variation have a broader pool of traits, increasing the likelihood that some individuals possess advantageous traits for the new environment.
In this scenario, a sudden shift in the availability of food sources—such as new vegetation or insects—would require organisms to adapt quickly to novel diets, foraging behaviors, or microhabitats. If population 2 lacks genetic variants that enable such adaptations (e.g., changes in digestive enzymes, behavior, or morphology), it may experience reduced survival and reproductive success. Over time, this can lead to a population decline or even local extinction.
Additionally, genetic bottlenecks and founder effects exacerbate this vulnerability. If population 2 has already undergone such events, it may possess high levels of inbreeding, which can reduce fitness due to increased expression of deleterious alleles.
Therefore, based on the relationship between genetic diversity and adaptability, the scientist’s claim that population 2 will be most severely affected is well-founded. Maintaining genetic diversity is crucial for populations to withstand and recover from environmental perturbations.
