Evaluate Evidence for Population Change - Biology

1. Which type of selection favors one extreme phenotype and shifts the mean?

   Directional selection. Population mean moves toward one end of the trait distribution.

2. Which selection pattern is indicated when the average phenotype becomes more common over time?

   Stabilizing selection. Selection against extremes increases frequency of intermediate phenotypes.

3. A trait has $p = 0.9$; what is the expected frequency of the recessive allele?

   $q = 0.1$. Allele frequencies must sum to 1, so $q = 1 - 0.9$.

4. Which evidence for evolution compares structures with similar anatomy due to common ancestry?

   Homologous structures. Same underlying structure from common ancestor, modified for different functions.

5. Which mechanism is most consistent with random allele loss after a population bottleneck?

   Genetic drift. Population bottlenecks reduce size, increasing random sampling effects.

6. Which selection pattern is indicated when one extreme phenotype increases in frequency over time?

   Directional selection. One extreme has higher fitness, shifting the population mean.

7. In Hardy–Weinberg terms, what does $p$ represent?

   Frequency of the dominant allele. Conventionally represents the more common or dominant allele frequency.

8. What are the five conditions required for Hardy–Weinberg equilibrium?

   No selection, no mutation, no migration, random mating, very large $N$. These conditions prevent allele frequency changes, maintaining equilibrium.

9. Which type of selection favors intermediate phenotypes and reduces extremes?

   Stabilizing selection. Average trait values are preserved while extremes are eliminated.

10. What is fitness in evolutionary biology?

    Relative reproductive success of a genotype or phenotype. Measured by survival and reproductive output compared to other genotypes.

11. Identify the evolutionary mechanism that changes allele frequencies by chance in small populations.

    Genetic drift. Random sampling effects are strongest when population size is limited.

12. Which result best supports natural selection if a heritable trait increases survival and becomes common?

    Trait-associated alleles increase in frequency over time. Higher survival leads to increased reproduction and allele transmission.

13. In Hardy–Weinberg terms, what does $q$ represent?

    Frequency of the recessive allele. Conventionally represents the less common or recessive allele frequency.

14. A population has $p = 0.4$; what is the expected homozygous recessive frequency?

    $q^2 = 0.36$. If $p = 0.4$, then $q = 0.6$, so $q^2 = 0.36$.

15. Find the homozygous dominant genotype frequency if $p = 0.6$.

    $p^2 = 0.36$. Square the dominant allele frequency: $0.6^2$.

16. Identify the evolutionary mechanism that moves alleles between populations.

    Gene flow (migration). Movement of individuals carries alleles between separate populations.

17. Which mechanism is most consistent with increased allele mixing after individuals immigrate?

    Gene flow. Immigration introduces new alleles and increases genetic mixing.

18. Which evidence for evolution is based on shared early developmental patterns among species?

    Comparative embryology. Early developmental similarities reveal shared ancestry despite adult differences.

19. A trait has $q^2 = 0.04$; what is the expected heterozygote frequency $2pq$?

    $2pq = 0.32$. If $q^2 = 0.04$, then $q = 0.2$, $p = 0.8$, so $2pq = 0.32$.

20. Which outcome indicates a population is evolving when compared to Hardy–Weinberg expectations?

    Observed genotype frequencies differ from expected frequencies. Deviations from Hardy-Weinberg predictions indicate evolutionary forces acting.

21. Which observation best supports genetic drift if allele frequencies change without fitness differences?

    Random allele frequency shifts, strongest in small populations. Random changes are more pronounced in smaller population sizes.

22. What is the definition of a species using the biological species concept?

    Groups that interbreed and produce fertile offspring. Reproductive compatibility determines species boundaries in this concept.

23. Which genotype frequency corresponds to homozygous dominant under Hardy–Weinberg?

    $p^2$. Probability of getting dominant allele from both parents equals $p \times p$.

24. What is the definition of a population in biology?

    Interbreeding members of the same species in one area. Geographic boundaries define the scope of genetic exchange.

25. Which genotype frequency corresponds to homozygous recessive under Hardy–Weinberg?

    $q^2$. Probability of getting recessive allele from both parents equals $q \times q$.

26. Which evidence best supports common ancestry if two species share many identical DNA sequences?

    High DNA sequence similarity (molecular homology). Genetic similarity indicates recent divergence from common ancestor.

27. Which conclusion is best supported if a trait is heritable and individuals with it leave more offspring?

    Natural selection can increase the trait's allele frequency. Heritable traits under selection will increase in frequency over generations.

28. Find the expected heterozygote frequency if $p = 0.5$ and $q = 0.5$.

    $2pq = 0.5$. When allele frequencies are equal, heterozygotes reach maximum frequency.

29. Which evidence best supports convergent evolution if two unrelated species share similar functions but not ancestry?

    Analogous structures. Similar function without shared ancestry indicates independent evolution.

30. Which selection pattern is indicated when both extremes increase and intermediates decrease?

    Disruptive selection. Intermediates have lower fitness than either extreme phenotype.

31. Find the heterozygote frequency if $p = 0.7$ and $q = 0.3$.

    $2pq = 0.42$. Multiply $2 \times 0.7 \times 0.3$ to get heterozygote frequency.

32. Which comparison best supports descent with modification if forelimb bones match across mammals?

    Homologous structures. Same bone pattern across species indicates common ancestral structure.

33. Which evidence for evolution compares similar features that evolved independently in similar environments?

    Analogous structures (convergent evolution). Similar functions evolved independently due to similar environmental pressures.

34. Which statement best defines evolution at the population level?

    Change in allele frequencies over time. Evolution occurs when allele proportions shift between generations.

35. Calculate $q$ if the recessive phenotype frequency is $q^2 = 0.36$.

    $q = 0.6$. Take the square root of the recessive phenotype frequency.

36. What is the definition of allele frequency in a population?

    Proportion of all gene copies that are a specific allele. Calculated by dividing copies of one allele by total gene copies in the population.

37. What is a vestigial structure evidence for?

    Descent with modification from ancestors. Reduced or nonfunctional structures inherited from functional ancestors.

38. Find the homozygous recessive genotype frequency if $q = 0.1$.

    $q^2 = 0.01$. Square the recessive allele frequency: $0.1^2$.

39. Which outcome indicates Hardy–Weinberg equilibrium if genotype frequencies match $p^2$, $2pq$, and $q^2$?

    No evidence of evolution for that gene in that population. Matching Hardy-Weinberg expectations indicates no evolutionary forces acting.

40. Calculate $p$ if the recessive phenotype frequency is $q^2 = 0.09$.

    $p = 0.7$. If $q^2 = 0.09$, then $q = 0.3$ and $p = 1 - 0.3 = 0.7$.

41. Which type of selection maintains multiple alleles because heterozygotes have highest fitness?

    Heterozygote advantage (balancing selection). Heterozygotes outperform both homozygotes, preserving both alleles.

42. State the Hardy–Weinberg genotype frequency equation.

    $p^2 + 2pq + q^2 = 1$. Expansion of $(p + q)^2$ gives genotype frequencies for diploid organisms.

43. What is the Hardy–Weinberg principle used to evaluate in populations?

    Whether a population is evolving (deviating from equilibrium). Compares observed frequencies to equilibrium expectations to detect evolution.

44. Identify the evolutionary mechanism that introduces new alleles by DNA change.

    Mutation. DNA errors during replication create novel alleles in populations.

45. Which genotype frequency corresponds to heterozygotes under Hardy–Weinberg?

    $2pq$. Two ways to get heterozygotes: dominant-recessive or recessive-dominant.

46. Which evidence for evolution is based on similarities in DNA or amino acid sequences?

    Molecular homology. DNA and protein similarities reflect shared evolutionary history.

47. State the Hardy–Weinberg allele frequency equation.

    $p + q = 1$. For a two-allele system, frequencies must sum to one.

48. Which evidence for evolution uses preserved remains and their ages to show change over time?

    Fossil record. Chronological sequence of fossils reveals morphological changes over time.

49. Which mechanism is most consistent with a new allele appearing after replication errors?

    Mutation. DNA replication errors create entirely new genetic variants.

50. Identify the best evidence for recent evolution if pesticide resistance rises in a pest population.

    A measurable increase in resistance allele frequency over generations. Direct measurement of evolutionary change through allele frequency shifts.

51. Which observation best supports gene flow as the cause if two populations become genetically similar?

    Increased migration accompanied by reduced allele frequency differences. Migration homogenizes allele frequencies between previously distinct populations.

52. Which type of selection favors both extremes and can create a bimodal distribution?

    Disruptive selection. Selection against intermediates can lead to population splitting.

53. Which term describes a change in allele frequencies in a population across generations?

    Microevolution. Evolution within a population, as opposed to macroevolution between species.

54. Calculate $p$ if the recessive allele frequency is $q = 0.2$.

    $p = 0.8$. Since $p + q = 1$, subtract $q$ from 1.

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