Analyze Population Data for Evolution - Biology

1. What is genotype frequency in a population?

   Proportion of individuals with a specific genotype. Calculated by dividing individuals with that genotype by total individuals.

2. What is frequency-dependent selection?

   Fitness depends on how common or rare a phenotype is. Selection strength varies with phenotype abundance in population.

3. What does it mean if allele frequency changes across generations in a dataset?

   Evolution is occurring in that population. Frequency changes indicate evolutionary forces are acting.

4. Calculate $p$ when $AA=36$, $Aa=48$, $aa=16$, and $N=100$.

   $p=0.60$. $p = \frac{2(36) + 48}{2(100)} = \frac{120}{200} = 0.60$

5. Identify the Hardy–Weinberg condition: what must be true about population size?

   Population is very large (minimizes genetic drift). Large populations reduce random sampling effects.

6. Choose the best evolutionary mechanism if allele frequencies change randomly after a population crash.

   Genetic drift (bottleneck effect). Population crashes cause random allele loss through sampling effects.

7. Choose the best evolutionary mechanism if a new island population has unusual allele frequencies from few founders.

   Genetic drift (founder effect). Few founding individuals create non-representative gene pools.

8. What is the operational definition of evolution in population genetics?

   Change in allele frequencies in a population over time. This is the quantitative definition used in population genetics studies.

9. What is a selective pressure in the context of population data?

   Environmental factor that causes differential survival or reproduction. Environmental factors create fitness differences between phenotypes.

10. Choose the best evolutionary mechanism if allele frequencies become more similar between two populations over time.

    Gene flow. Migration homogenizes allele frequencies between populations over time.

11. Identify the formula for allele frequency $p$ from genotype counts $AA$, $Aa$, $aa$ in $N$ individuals.

    $p=\frac{2AA+Aa}{2N}$. Counts each homozygote twice and heterozygote once for allele $A$.

12. Calculate expected $aa$ frequency when $q=0.20$ under Hardy–Weinberg equilibrium.

    $q^2=0.04$. $q^2 = (0.20)^2 = 0.04$

13. What is mutation as an evolutionary mechanism?

    Source of new alleles via DNA sequence changes. Introduces novel alleles but usually at low rates.

14. What is the Hardy–Weinberg equilibrium definition?

    Allele frequencies remain constant when no evolution occurs. Predicts frequencies when evolutionary forces are absent.

15. Calculate expected carrier (heterozygote) frequency when $q=0.10$ and $p=0.90$.

    $2pq=0.18$. $2pq = 2(0.90)(0.10) = 0.18$

16. Choose the best selection pattern if the mean phenotype increases steadily across generations.

    Directional selection. Consistent shift toward one extreme indicates directional selection.

17. Identify the allele frequency change if $p$ shifts from $0.50$ to $0.62$ in one generation.

    $\Delta p=0.12$. $\Delta p = 0.62 - 0.50 = 0.12$

18. What is nonrandom mating and how does it affect genotype frequencies?

    Mate choice/inbreeding changes genotype frequencies, not allele frequencies directly. Affects Hardy-Weinberg genotype predictions without changing allele frequencies.

19. What conclusion is supported if observed genotype frequencies differ from Hardy–Weinberg expectations?

    At least one Hardy–Weinberg condition is violated (evolution likely). Deviations indicate evolutionary forces are acting on the population.

20. Which populations experience stronger genetic drift: small or large?

    Small populations. Smaller populations have greater sampling variance.

21. Identify the Hardy–Weinberg condition: what must be true about mating?

    Mating is random. Prevents preferential mating patterns that alter genotype frequencies.

22. Calculate $p$ if $q=0.30$ for a two-allele locus under Hardy–Weinberg notation.

    $p=0.70$. Since $p + q = 1$, then $p = 1 - 0.30 = 0.70$

23. Calculate $q$ when $AA=36$, $Aa=48$, $aa=16$, and $N=100$.

    $q=0.40$. $q = \frac{2(16) + 48}{2(100)} = \frac{80}{200} = 0.40$

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

    $p^2$. Frequency of $AA$ genotype in Hardy-Weinberg equilibrium.

25. Which Hardy–Weinberg genotype frequency corresponds to heterozygotes?

    $2pq$. Frequency of $Aa$ genotype; factor of 2 accounts for both combinations.

26. Identify the strongest evidence for natural selection in population data across generations.

    Consistent allele frequency change correlated with a selective pressure. Correlation between selection pressure and frequency change indicates causation.

27. Identify the Hardy–Weinberg condition: what must be true about mutation?

    No mutations occur. Mutations would change allele frequencies over time.

28. Identify the Hardy–Weinberg condition: what must be true about migration (gene flow)?

    No migration; no gene flow into or out of the population. Migration introduces or removes alleles from the population.

29. Which inference is supported if a beneficial allele rises quickly in frequency after an environmental change?

    Positive selection increased the allele's frequency. Rapid increase after environmental change indicates adaptive advantage.

30. What is an allele frequency in a population?

    Proportion of all gene copies that are a specific allele. Calculated by dividing copies of that allele by total gene copies.

31. What conclusion is supported if observed genotype frequencies match Hardy–Weinberg expectations?

    No evidence of evolution at that locus in that population. Meeting Hardy-Weinberg expectations indicates no evolutionary change.

32. Identify the Hardy–Weinberg condition: what must be true about natural selection?

    No natural selection; equal fitness among genotypes. All genotypes must have equal reproductive success.

33. What is natural selection in terms of population data?

    Nonrandom allele frequency change due to differential survival/reproduction. Fitness differences cause predictable frequency changes.

34. Choose the best selection pattern if extremes decline and intermediate phenotypes become most common.

    Stabilizing selection. Intermediate optimization indicates selection against extremes.

35. What is heterozygote advantage?

    Heterozygotes have highest fitness, maintaining both alleles. Balancing selection maintains genetic diversity.

36. Calculate expected $AA$ frequency when $p=0.70$ under Hardy–Weinberg equilibrium.

    $p^2=0.49$. $p^2 = (0.70)^2 = 0.49$

37. Calculate $q$ if the recessive phenotype frequency is $0.09$ and the trait is recessive.

    $q=0.30$. Since $q^2 = 0.09$, then $q = \sqrt{0.09} = 0.30$

38. What is the key population-level evidence that a trait is heritable?

    Trait variation correlates between parents and offspring. Parent-offspring correlation indicates genetic basis for the trait.

39. State the Hardy–Weinberg genotype frequency equation for two alleles.

    $p^2+2pq+q^2=1$. Expands $(p+q)^2$ to show all genotype frequencies.

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

    $q^2$. Frequency of $aa$ genotype in Hardy-Weinberg equilibrium.

41. What is genetic drift?

    Random change in allele frequencies due to chance. Sampling error causes unpredictable frequency changes.

42. Which inference is supported if a phenotype is rare and has higher fitness specifically because it is rare?

    Negative frequency-dependent selection. Rare phenotypes gain advantage specifically from their rarity.

43. State the Hardy–Weinberg allele frequency equation for two alleles.

    $p+q=1$. The two allele frequencies must sum to 1.

44. Choose the best selection pattern if both extremes increase while intermediates decrease in frequency.

    Disruptive selection. Both extremes increasing indicates selection against intermediate forms.

45. What is the gene pool of a population?

    All alleles present in the population. The collective genetic variation available for evolution.

46. Calculate expected heterozygote frequency when $p=0.60$ and $q=0.40$.

    $2pq=0.48$. $2pq = 2(0.60)(0.40) = 0.48$

47. Which inference is supported if a harmful allele persists because heterozygotes have higher fitness?

    Balancing selection via heterozygote advantage. Heterozygote advantage maintains harmful alleles in populations.

48. What is gene flow (migration) in evolutionary biology?

    Movement of alleles between populations via migration and breeding. Homogenizes allele frequencies between connected populations.

49. Identify the formula for allele frequency $q$ from genotype counts $AA$, $Aa$, $aa$ in $N$ individuals.

    $q=\frac{2aa+Aa}{2N}$. Counts each homozygote twice and heterozygote once for allele $a$.

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