Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Natural Selection: The process by which individuals with favorable phenotypes are more likely to survive and reproduce, passing their advantageous alleles to the next generation.
Variation: Differences between individuals of the same species, caused by genetic factors (mutation, meiosis) and environmental factors. Genetic variation is essential for natural selection to act upon.
Adaptation: An inherited feature that increases an organism's fitness (chance of survival and reproduction) in its environment.
Stabilizing Selection: A type of natural selection that favors intermediate phenotypes and acts against extreme variants, maintaining the status quo (e.g., human birth weight).
Directional Selection: A type of selection that favors one extreme phenotype over others, causing the allele frequency to shift over time in that direction (e.g., antibiotic resistance in bacteria like ).
Disruptive Selection: Selection that favors individuals at both extremes of the phenotypic range over intermediate phenotypes, which can lead to speciation.
Artificial Selection (Selective Breeding): The process by which humans choose individuals with desirable traits (e.g., high crop yield, domestic docility) and breed them together over many generations.
Inbreeding Depression: A disadvantage of artificial selection where a lack of genetic diversity leads to the accumulation of harmful recessive alleles in the population.
Selection Pressure: External factors (like predation, disease, or competition) that affect an organism's ability to survive in a given environment.
Antibiotic Resistance: An example of rapid evolution where the use of antibiotics acts as a selection pressure, favoring mutant bacteria that possess resistance genes (e.g., ).
📐Formulae
💡Examples
Problem 1:
In a population of mice, the frequency of the recessive allele for white fur () is . Assuming the population is in Hardy-Weinberg equilibrium, calculate the percentage of the population that is heterozygous () for fur color.
Solution:
Explanation:
Given . Since , we find . The frequency of the heterozygous genotype is represented by in the Hardy-Weinberg equation. Therefore, . To convert to a percentage: .
Problem 2:
Explain how the use of antibiotics leads to the development of resistant strains such as through natural selection.
Solution:
Selection pressure and allele survival.
Explanation:
Within a bacterial population, random mutations occur. Some mutations may confer resistance to an antibiotic. When the antibiotic is applied, it acts as a selection pressure, killing non-resistant bacteria. The resistant individuals survive and reproduce asexually via binary fission, passing the resistance allele to their offspring. Over generations, the frequency of the resistance allele increases, leading to a population of ().
Problem 3:
Compare Natural Selection and Artificial Selection in terms of the 'agent' of selection and the end result for the species.
Solution:
Agent: Environment vs. Humans; Result: Survival vs. Utility.
Explanation:
In Natural Selection, the agent is the environment (predators, climate), and the result is increased biological fitness and survival. In Artificial Selection, the agent is humans, and the result is the enhancement of specific traits useful to humans (e.g., more milk from ), which may actually decrease the organism's fitness in the wild.