Natural Selection Effects - Middle School Life Science

1. Which evidence best supports natural selection: a trait becomes more common after a new predator arrives?

   A trait becomes more common after a new predator arrives. Shows selective advantage against new predation pressure.

2. What is stabilizing selection?

   Selection that favors intermediate traits, reducing variation. Eliminates extremes, maintaining average trait values.

3. What is the definition of fitness in natural selection?

   Reproductive success relative to others in the same environment. Measured by number of viable offspring produced.

4. What is the main difference between natural selection and genetic drift?

   Selection is nonrandom; drift changes frequencies by chance. Selection is fitness-based; drift is random sampling error.

5. Which graph shape matches directional selection on beak size over time: mean shifts left or stays centered?

   Mean shifts left or right (it does not stay centered). Directional selection shifts the trait distribution.

6. Which condition is required for natural selection to occur: heritable variation or identical traits?

   Heritable variation. Without variation, selection cannot favor any traits.

7. Which statement is correct: individuals evolve or populations evolve?

   Populations evolve. Evolution is change in allele frequencies over generations.

8. Which conclusion is supported: Trait A has $2\times$ higher offspring survival than Trait B for 5 generations.

   Trait A frequency should increase over generations. Higher reproductive success leads to increased frequency over time.

9. What is disruptive selection?

   Selection favors both extremes over the average phenotype. Can split a population into two distinct groups.

10. Identify the correct statement about evolution: Does natural selection create new traits?

    No; it selects among existing heritable variation. Selection only acts on variation from mutation and recombination.

11. What is the difference between genotype and phenotype?

    Genotype is genetic makeup; phenotype is observable traits. Genotype determines phenotype through gene expression.

12. What is disruptive selection?

    Selection that favors both extremes, increasing variation. Eliminates intermediate values, creating two distinct groups.

13. What is trait distribution in a population?

    How common different trait forms are within the population. Shows the frequency of each trait variant in the population.

14. Identify the best evidence for selection (not drift): a consistent trait advantage repeats in many populations.

    Repeated consistent trait advantage across many populations. Drift would show random patterns across populations.

15. Identify the selection type: after drought, birds with larger beaks become more common.

    Directional selection. Larger beaks are advantageous, shifting population toward that extreme.

16. What does it mean for a trait to be heritable?

    It can be passed from parents to offspring through genes. Genetic inheritance allows traits to persist across generations.

17. What three conditions must be present for natural selection to occur?

    Variation, heritability, and differential reproductive success. These three factors enable evolution by natural selection.

18. What is the role of variation in natural selection?

    Variation provides different traits for selection to act upon. No variation means no differential survival or reproduction.

19. What is fitness in natural selection?

    Relative reproductive success in a specific environment. Organisms with higher fitness leave more offspring with their traits.

20. What is the relationship between mutation and natural selection?

    Mutation creates new variation; selection filters existing variation. Mutation provides raw material; selection determines which variants succeed.

21. What is the difference between adaptation and acclimation?

    Adaptation is inherited over generations; acclimation is individual change. Adaptations are genetic; acclimation is temporary response to environment.

22. What is the key requirement for a trait to be shaped by natural selection?

    The trait must be heritable (genetically passed to offspring). Only genetic traits can be passed on and selected for over time.

23. Identify the best evidence for selection: trait helps survival, and its frequency rises over time.

    Natural selection is increasing the advantageous trait frequency. Both conditions (advantage + frequency change) prove selection is occurring.

24. What does it mean if a trait increases in frequency after an environmental change?

    The trait likely increased fitness under the new conditions. Natural selection favors traits suited to new environment.

25. Identify the correct claim: natural selection acts on individuals or changes populations over generations?

    It changes populations over generations. Selection acts on individuals but evolution occurs in populations.

26. What is directional selection?

    Selection favors one extreme, shifting the average trait value. Population mean shifts toward the favored extreme.

27. Identify the type of selection: very small and very large fish are eaten; medium fish survive best.

    Stabilizing selection. Extremes removed by predation, average size optimal.

28. Which statement best describes how natural selection changes trait distribution?

    Beneficial heritable traits become more common over generations. Selection increases frequency of advantageous traits over time.

29. Identify the selection type: the darkest mice become most common on dark lava rock.

    Directional selection. One extreme (darkest) is favored over lighter colors.

30. What is meant by trait distribution in a population?

    How common different trait forms are among individuals. Measures the frequency of different versions of a trait in a population.

31. Identify the best conclusion: A heritable trait increases from $20\%$ to $60\%$ after drought.

    The trait likely increased fitness under drought conditions. Large frequency increase suggests strong selective advantage.

32. What is directional selection?

    Selection that favors one extreme, shifting the average trait value. Pushes population toward one extreme trait value.

33. What is natural selection?

    Differential survival and reproduction based on heritable traits. Organisms with favorable traits survive and reproduce more.

34. Identify the selection type: average birth weight has highest survival; very low and very high decrease.

    Stabilizing selection. Selection against extremes maintains intermediate trait values.

35. What type of selection favors both extremes and can split a population into two groups?

    Disruptive selection. Creates bimodal distribution by selecting against intermediate forms.

36. Which option is the strongest evidence of selection: A) learned behavior spreads, B) heritable trait frequency changes?

    B) Heritable trait frequency changes. Learned behaviors aren't inherited; only genetic changes show evolution.

37. What condition must be true for natural selection to change trait frequencies?

    Trait variation must be heritable and affect fitness. Only heritable traits that impact survival/reproduction can evolve.

38. Identify the type of selection: after drought, birds with larger beaks become more common.

    Directional selection. Larger beaks selected for when food requires them.

39. Identify the selection type: only very small and very large beaks succeed; medium beaks decline.

    Disruptive selection. Both extremes succeed while intermediate forms are selected against.

40. What does fitness mean in natural selection?

    Relative reproductive success in a specific environment. Measures how well an organism reproduces compared to others.

41. What type of selection shifts the population average toward one extreme trait value?

    Directional selection. Favors one extreme (e.g., darkest moths in polluted areas).

42. What is the difference between genotype and phenotype?

    Genotype is genetic makeup; phenotype is observable traits. Genes determine genotype; their expression creates phenotype.

43. What condition must be true for a trait to be acted on by natural selection?

    The trait must be heritable (genetically passed to offspring). Only genetic traits can be passed on and selected for.

44. Identify the correct claim: Natural selection acts on individuals or on populations?

    Individuals are selected; populations evolve (trait frequencies change). Selection affects individual fitness; evolution occurs in populations.

45. Identify the selection type: average beak size increases as only large seeds remain.

    Directional selection. Larger beaks are favored when only large seeds are available.

46. What is meant by trait distribution in a population?

    How common each trait or phenotype is within the population. Measures the relative frequency of different traits.

47. Identify the type of selection: in patchy habitat, light and dark mice survive; medium mice are seen.

    Disruptive selection. Different habitats favor different camouflage colors.

48. Which evidence most directly shows natural selection is occurring in a population?

    A heritable trait becomes more common across generations. Frequency change over time proves selection is acting on the trait.

49. A trait increases survival but is not heritable. What conclusion best fits the evidence?

    It will not increase by natural selection across generations. Selection only acts on heritable traits that can be passed to offspring.

50. Identify the evidence-based conclusion: a trait increases from $20\%$ to $60\%$ in 10 generations.

    The trait likely increased fitness under the current conditions. Large frequency increase suggests strong positive selection.

51. Which dataset pattern is evidence of selection: random trait change or consistent increase in one trait with higher survival?

    Consistent increase in one trait with higher survival. Non-random pattern indicates selection, not chance.

52. What is stabilizing selection?

    Selection favors the average and reduces extreme phenotypes. Maintains the population mean by eliminating extremes.

53. Which evidence best supports natural selection: individuals change or populations change?

    Populations change in trait frequencies over generations. Evolution occurs at population level, not individual level.

54. Identify the best conclusion: after a drought, deeper-beaked birds leave more offspring.

    Drought favored deeper beaks, so deep-beak frequency should rise. Environmental change created selection for the adaptive trait.

55. Identify the selection type: light and dark mice survive on patchy habitat; medium color is eaten most.

    Disruptive selection. Both extremes survive better than intermediate forms in patchy environments.

56. Choose the best inference: survivors have trait X and produce more offspring; what happens to trait X frequency?

    Trait X frequency increases in the next generations. Higher reproductive success increases trait frequency.

57. What is adaptation in the context of natural selection?

    A heritable trait that increases fitness in an environment. Results from selection favoring beneficial traits over time.

58. Which option is the strongest evidence that a trait is adaptive: A) common trait B) trait increases survival?

    B) Trait increases survival (and reproduction) in that environment. Fitness advantage is the defining feature of adaptations.

59. Which option is the strongest evidence that a trait is heritable: similarity to parents or to habitat?

    Similarity to parents (offspring resemble parents for the trait). Parent-offspring resemblance indicates genetic inheritance.

60. Identify the selection type: very small and very large individuals survive poorly; medium survives best.

    Stabilizing selection. Medium size has highest fitness; extremes are selected against.

61. Which option is the best evidence for selection: A) random change B) trait linked to higher offspring number?

    B) Trait linked to higher offspring number. Reproductive advantage directly demonstrates natural selection.

62. What is the difference between phenotype and genotype?

    Phenotype is expressed traits; genotype is genetic makeup. Phenotype is observable; genotype is the underlying DNA.

63. Which statement best explains why individuals do not evolve by natural selection?

    Selection changes trait frequencies in populations, not individuals. Evolution acts on populations through differential reproduction.

64. What does fitness mean in natural selection?

    Relative reproductive success in a specific environment. Not just survival, but how many offspring survive to reproduce.

65. What does it mean when a trait is heritable?

    It can be passed from parents to offspring through genes. Genetic inheritance allows traits to persist across generations.

66. Which type of evidence best supports natural selection in a population over time?

    A consistent change in trait frequency across generations. Shows non-random change driven by differential fitness.

67. What type of selection favors intermediate trait values and reduces extremes?

    Stabilizing selection. Reduces variation by selecting against both extremes.

68. What is genetic variation, and why is it necessary for natural selection?

    Differences in genes/traits; selection cannot act without variation. Without different traits to select from, evolution cannot occur.

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