Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Natural selection can only occur if there is variation among members of the same species, which is generated by , , and .
During , variation is produced by crossing over in and independent assortment of bivalents in .
Adaptations are characteristics that make an individual suited to its environment and way of life; these traits are heritable and passed to offspring.
Species tend to produce more offspring than the environment can support, leading to a struggle for survival and competition for resources.
Individuals that are better adapted tend to survive and produce more offspring, while the less well-adapted tend to die or produce fewer offspring ().
Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics, leading to changes within the species over time.
Evolution is the cumulative change in the heritable characteristics of a population, which is fundamentally a change in over generations.
📐Formulae
💡Examples
Problem 1:
On the island of Daphne Major, the medium ground finch () experienced a severe drought in . The population dropped from to . Calculate the impact of selection if the average beak depth changed from mm to mm.
Solution:
The mean beak depth increased by mm. Using the selection differential formula , we find .
Explanation:
During the drought, small, soft seeds became scarce, while large, hard seeds remained. Finches with larger beak depths were better adapted to crack the hard seeds, leading to . The survivors passed the alleles for larger beaks to their offspring, shifting the population's phenotype.
Problem 2:
Explain the development of antibiotic resistance in using the principles of natural selection.
Solution:
A population of bacteria is exposed to . Initially, a small number of bacteria possess a mutation in the gene, granting resistance (). In the presence of the antibiotic, non-resistant bacteria die (), while resistant individuals survive () and reproduce via binary fission.
Explanation:
The antibiotic acts as the selection pressure. Because the phenotype has a higher fitness in an environment containing the drug, the frequency of the allele increases rapidly across generations, rendering the antibiotic ineffective.