📝 Heritable variation in natural selection (9 MCQs)
📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 9 questions available
What is Heritable variation in natural selection?
Definition:
Heritable variation is the presence of differences in traits among individuals in a population that are transmitted from parents to offspring through genetic material (DNA), and it is the raw material for natural selection, providing the diversity upon which environmental pressures act, and it arises from mutations, gene recombination, and genetic drift.
Working:
Heritable variation works by generating a range of phenotypes (physical traits) in a population, where the genetic diversity is maintained through sexual reproduction (meiosis) and mutations, and the variation is often described by the equation , where is heterozygosity and is the frequency of alleles, and when the environment changes, individuals with advantageous variants are more likely to survive and reproduce, changing allele frequencies in the next generation.
Example:
A simple example is the color variation in peppered moths (Biston betularia), where a genetic mutation produced a dark (melanic) form, and during the Industrial Revolution, when soot darkened trees, the dark form had higher survival due to better camouflage, and over time, the frequency of the dark allele increased in the population, demonstrating heritable variation and natural selection.
Reason:
Heritable variation is essential because without it, natural selection cannot act, and populations would remain static, and understanding variation is crucial for evolutionary biology, conservation genetics, and agriculture, as it determines a species' ability to adapt to changing conditions and to disease.
📝 All Heritable variation in natural selection MCQs
Q1. A population of beetles contains individuals with different shell colors. After mating only beetles with dark shells, the offspring contain a much higher proportion of dark-shelled beetles. Which conclusion is best supported?
📖 Explanation: The offspring resemble selected parents more often than expected by chance, providing evidence that variation in shell color has a heritable component. This does not by itself prove that the trait is entirely genetic or advantageous.
Q2. Two groups of plants have different leaf sizes. Group A is grown in shade and Group B in sunlight. Their offspring are later grown under identical conditions, and the offspring still differ in average leaf size. What interpretation is most reasonable?
📖 Explanation: Because the offspring were raised under the same conditions yet retained differences associated with their parental groups, inherited factors are a plausible explanation. Environmental effects cannot be completely ruled out without further controlled breeding experiments.
Q3. A farmer notices that some sheep naturally produce more wool than others. He breeds high-wool producers for several generations, and average wool production increases. Which reasoning best explains the result?
📖 Explanation: Selection can change a population when individuals differ in a trait and at least part of that variation is inherited. Repeatedly breeding high-producing sheep increases the representation of inherited factors associated with greater wool production.
Q4. A student argues, 'If two siblings have different heights, height variation cannot be heritable because they have the same parents.' What is the strongest criticism of this reasoning?
📖 Explanation: Having the same parents does not make siblings genetically identical. They receive different combinations of parental alleles, while environmental factors may also contribute. Therefore, variation among siblings is compatible with a heritable component.
Q5. A population has two inherited forms of a trait. Before selection, the forms occur at frequencies 0.50 and 0.50. After several generations, the first form becomes 0.80. Which observation would most strongly support the idea that inheritance contributed to this change?
📖 Explanation: A sustained increase accompanied by greater reproductive success and resemblance between parents and offspring provides evidence linking the trait to both selection and inheritance. Appearance alone or temporary environmental changes would provide weaker support.
Q6. Researchers record the average body size of offspring from parents with different body sizes. The data show: parent size 10 cm → offspring 11 cm; 15 cm → offspring 14 cm; 20 cm → offspring 18 cm; 25 cm → offspring 22 cm. What pattern is most strongly indicated?
📖 Explanation: The offspring averages generally rise as parental size increases, showing a positive parent-offspring association. Because the relationship is not perfect, the pattern suggests partial heritability rather than complete genetic determination of body size.
Q7. A researcher finds that two genetically different strains of plants grow to different average heights in the same greenhouse. However, when each strain is grown under several nutrient levels, their heights overlap substantially. What conclusion is most justified?
📖 Explanation: Different average heights under identical conditions indicate a genetic contribution, while substantial overlap across nutrient conditions shows environmental influence. Many biological traits result from interactions between inherited variation and environmental conditions rather than one factor alone.
Q8. A biologist compares two populations of insects. Population X shows large variation in wing length, but offspring wing length is weakly associated with parental wing length. Population Y shows less variation, but offspring strongly resemble their parents in wing length. Which population provides the stronger basis for predictable inherited differences in wing length?
📖 Explanation: Heritable variation requires both differences among individuals and transmission of some differences to offspring. Population Y has stronger evidence of inheritance because offspring resemble parents more consistently, even though its overall trait variation is smaller.
Q9. In a hypothetical population, a trait varies continuously from low to high values. Individuals at the high end are more likely to reproduce, and their offspring tend to have higher trait values than average. Which prediction follows most logically if this pattern continues for many generations?
📖 Explanation: The reasoning requires combining variation, differential reproductive success, and inheritance. If individuals with higher values consistently leave more offspring and offspring tend to resemble them, inherited variants associated with higher values should become more common, shifting the population average.