- In a population of mice, coat color affects survival on dark soil. Survival probabilities are: black coat 0.60 and tan coat 0.40. If these probabilities stay similar for many generations, what is the most likely trend in the population?
Answer: Black coat frequency will tend to increase because black mice have a higher probability of surviving and reproducing.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. With survival probabilities of black: 0.60 and tan: 0.40, black mice have 50% higher survival (0.60/0.40 = 1.5×). Over many generations, this consistent survival advantage means more black mice survive to reproduce each generation, gradually increasing black coat frequency. Choice C correctly predicts black coat frequency will tend to increase because black mice have higher probability of surviving and reproducing. Choice B incorrectly claims 60% vs 40% isn't large enough (a 50% survival advantage is quite significant!), while A illogically suggests lower survival leads to increased frequency. Predicting long-term trends: (1) IDENTIFY survival: Black: 60%, Tan: 40%. (2) CALCULATE advantage: Black mice have 1.5× survival rate (50% advantage). (3) PREDICT trend: Black coat → frequency INCREASES over time. Tan coat → frequency DECREASES over time. (4) ASSESS pace: 20 percentage point difference → moderate selection → steady change. After many generations, the population will become predominantly black-coated, matching the dark soil for better camouflage!
- A rabbit population has a gene with alleles H and h. During a harsh winter, HH rabbits have a 55% chance of surviving to reproduce, Hh have a 50% chance, and hh have a 45% chance. Compared with a situation where HH survival is 95% and hh survival is 5%, how would you describe the strength of selection in the harsh-winter case?
Answer: Selection is weaker in the harsh-winter case because survival probabilities are similar across genotypes
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates predictable changes in allele frequencies: small differences (55% HH, 50% Hh, 45% hh) mean weaker selection and slower change compared to large gaps (95% vs 5%). The direction of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the rate depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). In the harsh winter, survival rates are close across genotypes (only 10% max difference), so selection is weaker than in the extreme case with an 90% gap, leading to slower frequency changes. Choice B correctly describes selection as weaker in the harsh-winter case because survival probabilities are similar across genotypes, focusing on the small probability differences. Choice A fails by claiming stronger selection due to overall low survival, missing that strength depends on relative differences, not absolute levels. Predicting frequency changes from probabilities: (1) Identify and compare differences: harsh winter small (10 points) vs other large (90 points). (2) Compare: smaller gap = weaker. (3) Predict: both favor H, but harsh winter slower. (4) Assess magnitude: Small difference means weak selection, like slow evolution of fur thickness in rabbits during mild climate shifts!
- In a population of beetles, color is controlled by a gene with two alleles: G (green) and g (brown). A pesticide is applied. Individuals with genotypes GG and Gg have a 90% chance of surviving to reproduce, while gg individuals have a 20% chance of surviving. Without doing any Hardy-Weinberg calculations, which allele is expected to increase in frequency in the next generation, and why?
Answer: Allele G will increase because genotypes containing G have a higher survival probability and contribute more offspring.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The DIRECTION of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the RATE depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). Example: if 100 bacteria, 10 resistant (10%) and 90 susceptible (90%), antibiotic kills 95% of susceptible (only ~5 survive) but kills only 10% of resistant (9 survive), then next generation starts with ~5 susceptible + ~9 resistant = ~14 total, with ~64% resistant (9/14)—resistance frequency jumped from 10% to 64% in one generation due to huge survival probability difference! This probability-based frequency change IS evolution by natural selection! In this beetle population, genotypes with G (GG and Gg) have 90% survival, while gg has 20%, so G-carrying individuals are much more likely to survive and reproduce, leading to an increase in G frequency over time. Choice B correctly predicts that allele G will increase because genotypes containing G have higher survival probability and contribute more offspring. Choice A fails by incorrectly assuming rare alleles always increase, ignoring that selection favors alleles with higher survival probabilities regardless of rarity. Predicting frequency changes from probabilities: (1) IDENTIFY survival/reproduction probabilities for each variant: G-containing: 90% survive, gg: 20% survive. (2) COMPARE probabilities: G-containing has higher survival → more survive to reproduce. (3) PREDICT direction: Higher probability variant (G) → frequency INCREASES. Lower (g) → DECREASES. (4) ASSESS magnitude: LARGE difference (90% vs 20% = 70 points) → RAPID change. Keep practicing these steps, and you'll master predicting evolution like a pro! - In a bird species, a gene has two alleles, A and a. A new predator arrives. Birds with genotype AA have a 60% chance of surviving to reproduce, Aa have a 60% chance, and aa have a 30% chance. Which statement best predicts how allele frequencies will change over generations if these survival rates continue?
Answer: Allele A will increase because genotypes carrying A survive more often than aa
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates predictable changes in allele frequencies: if individuals with allele A (AA and Aa) have 60% survival while aa have 30% (notable difference), then A-carrying individuals contribute more offspring, causing A frequency to increase and a to decrease. The direction of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the rate depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). Here, the predator introduces selection where AA and Aa birds survive at 60% (same rate), but aa at only 30%, so over generations, more A alleles will be passed on as aa individuals are less likely to reproduce, increasing A frequency. Choice B correctly predicts that allele A will increase because genotypes carrying A survive more often than aa, recognizing the selection against the recessive homozygote. Choice C fails by claiming no change since AA and Aa have the same survival, ignoring that the lower survival of aa still drives A frequency up. Predicting frequency changes from probabilities: (1) Identify survival: AA 60%, Aa 60%, aa 30%. (2) Compare: A-carriers higher than aa. (3) Predict direction: A increases, a decreases. (4) Assess magnitude: 30% difference means moderate selection strength. Real-world example: like sickle-cell anemia, where heterozygotes have malaria resistance (higher survival), leading to balanced frequencies in affected regions! - Two versions of a lizard color trait exist: light and dark. In Habitat 1 (light sand), light lizards survive to reproduce at 0.90 and dark lizards at 0.10. In Habitat 2 (dark rock), light lizards survive at 0.55 and dark lizards at 0.45. In which habitat will the color trait frequencies change more rapidly due to natural selection?
Answer: Habitat 1, because the survival difference is much larger (stronger selection causes faster change).
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The key here is comparing the MAGNITUDE of selection: Habitat 1 has survival differences of 0.90 vs 0.10 (80 percentage point difference), while Habitat 2 has 0.55 vs 0.45 (only 10 percentage point difference). Larger probability differences mean stronger selection and faster evolution! Choice B correctly identifies that Habitat 1's much larger survival difference causes faster frequency change. Choice A reverses the logic (closer probabilities mean WEAKER selection, not stronger), while C incorrectly claims all selection causes equally fast change. Predicting rate of change: Habitat 1: 90% vs 10% survival = 80 point difference → STRONG selection → RAPID change. Habitat 2: 55% vs 45% survival = 10 point difference → WEAK selection → SLOW change. Think of it like this: In Habitat 1, for every 10 dark lizards, only 1 survives, while 9 of 10 light lizards survive—a 9:1 survival ratio! In Habitat 2, it's roughly 1.2:1—much less dramatic. The extreme selection in Habitat 1 will rapidly shift the population toward light coloration!
- A fish population has two phenotypes: striped and unstriped. In clear water, striped fish avoid predators better. Each generation, 70% of striped fish survive to reproduce, but only 35% of unstriped fish survive to reproduce. What is the best prediction about the striped phenotype frequency over time (assuming the trait is heritable)?
Answer: Striped fish become more common because they have a higher probability of surviving to reproduce
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates predictable changes in allele frequencies: striped fish at 70% survival vs unstriped at 35% (double the probability) means striped contribute more offspring, increasing their frequency. The direction of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the rate depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). In clear water, the better camouflage of striped fish gives them a 70% survival to reproduction vs 35% for unstriped, so over time, the striped phenotype (and its alleles) will become more frequent in the population. Choice A correctly predicts striped fish become more common because they have a higher probability of surviving to reproduce, connecting survival odds to frequency increase. Choice B fails by suggesting they become less common due to predator focus, which contradicts the given higher survival data. Predicting frequency changes from probabilities: (1) Identify survival: striped 70%, unstriped 35%. (2) Compare: striped higher. (3) Predict direction: striped increases. (4) Assess magnitude: 35% difference means moderate to strong selection, like guppy color patterns evolving under predation pressure in streams!
- A bacterial population contains two types: antibiotic-resistant (R) and susceptible (S). Before treatment, 10% are R and 90% are S. During antibiotic treatment, 95% of S die, but only 5% of R die. After treatment, what happens to the frequency of R among the surviving bacteria?
Answer: It increases because R has a much higher probability of survival than S.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The DIRECTION of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the RATE depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). Here, with 95% of S dying (5% survive) versus only 5% of R dying (95% survive), the huge survival probability difference means far more R bacteria survive to form the next generation, jumping R's frequency from 10% to much higher, like from 10% to around 64% in a similar example. Choice A correctly predicts the increase in R frequency by recognizing that its much higher survival probability leads to a disproportionate contribution to survivors. Choice B fails by mistakenly thinking antibiotics make bacteria susceptible, but actually, selection removes susceptible ones, increasing resistant frequency—don't worry, you're building a strong understanding! Remember this strategy: (1) IDENTIFY probabilities: R 95% survive, S 5%; (2) COMPARE: R much higher; (3) PREDICT: R increases, S decreases; (4) ASSESS: large difference means rapid change, as in real antibiotic resistance where frequencies skyrocket quickly.
- In a lizard population, a gene has alleles H and h. Under normal conditions (no new predators, no drought, no disease), survival and reproduction are similar for all genotypes, so allele frequencies are stable. If conditions remain the same, what does Hardy-Weinberg equilibrium predict about allele frequencies?
Answer: They will stay approximately constant because no selection (or other forces) is acting
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The DIRECTION of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the RATE depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). In this lizard population under normal conditions with no selection pressures, all genotypes have similar survival and reproduction—this means NO differential probabilities, so no genotype contributes disproportionately to the next generation, and Hardy-Weinberg equilibrium predicts allele frequencies remain constant over time. Choice A correctly predicts that allele frequencies will stay approximately constant because no selection (or other evolutionary forces) is acting—this is the fundamental prediction of Hardy-Weinberg equilibrium. Choice B incorrectly suggests rare alleles are favored (no mechanism for this without selection), C wrongly claims evolution always happens (it requires differential survival/reproduction or other forces), and D misunderstands that mate choice patterns alone don't change allele frequencies without differential reproduction. Predicting frequency changes from probabilities: (1) IDENTIFY survival/reproduction probabilities: All genotypes have SIMILAR survival and reproduction. (2) COMPARE probabilities: NO significant differences between genotypes. (3) PREDICT direction: No probability differences → NO directional change in frequencies. (4) This is Hardy-Weinberg equilibrium: when survival/reproduction probabilities are equal, allele frequencies stay constant! The five conditions for Hardy-Weinberg: no selection (equal survival/reproduction), no mutation, no migration, large population (no drift), random mating. When these hold, allele frequencies remain stable generation after generation—evolution requires breaking at least one condition!
- A plant species has two flower-color alleles, P and p. Pollinators visit purple flowers more often, so plants with at least one P allele produce more seeds. Seed production (average offspring) is: PP: 40 seeds, Pp: 40 seeds, pp: 20 seeds. Over several generations, what is the most likely change in allele frequencies?
Answer: Allele P will increase because genotypes with P have higher reproductive success.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. Here we have reproductive differences: PP: 40 seeds, Pp: 40 seeds, pp: 20 seeds. Plants with at least one P allele produce twice as many offspring as pp plants, meaning P-containing genotypes contribute more alleles to the next generation, causing P frequency to increase. Choice C correctly predicts frequency changes by recognizing higher reproductive success for genotypes with P leads to increasing P frequency. Choice A incorrectly thinks pp will "catch up" (they won't—they consistently produce fewer offspring), while B wrongly claims reproduction differences don't affect evolution (they're a key driver!). Predicting frequency changes from reproduction: (1) IDENTIFY reproduction rates: PP and Pp: 40 seeds each, pp: 20 seeds. (2) COMPARE: P-carriers produce 2× more offspring than pp. (3) PREDICT: P allele → frequency INCREASES (more offspring = more P alleles passed on). p allele → frequency DECREASES (fewer offspring from pp). This 2× reproduction difference creates strong selection for purple flowers! - In a bird species, beak type is controlled by alleles B and b. A new hard-seeded plant becomes common. Birds with BB have a 70% chance to survive the season, Bb have 60%, and bb have 20%. Which prediction is most consistent with natural selection?
Answer: Allele B will become more common because birds with B (especially BB and Bb) survive more often and can reproduce.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if birds with allele B have higher survival probabilities (BB: 70%, Bb: 60%) compared to bb birds (20%), then B-carrying birds contribute disproportionately more offspring to next generation, causing B allele frequency to INCREASE and b allele frequency to DECREASE. The large survival advantage for B-containing genotypes (70% and 60% vs 20%) indicates strong selection. Choice A correctly predicts that allele B will become more common because birds with B (especially BB and Bb) survive more often and can reproduce, passing on more B alleles to the next generation. Choice B incorrectly suggests surviving bb birds will be "stronger"—survival probability affects frequency, not individual strength; C wrongly claims survival doesn't affect reproduction when dead birds can't reproduce; D falsely states individuals change their alleles when alleles are fixed at conception. Predicting frequency changes: (1) IDENTIFY survival probabilities: BB: 70%, Bb: 60%, bb: 20%. (2) COMPARE: B-containing genotypes have MUCH HIGHER survival. (3) PREDICT: B frequency INCREASES, b frequency DECREASES. (4) ASSESS: Large survival differences (50 percentage points between BB and bb) indicate STRONG selection for B allele. This exemplifies adaptive evolution in response to environmental change! - In a fish species, a gene has two alleles: F and f. In polluted water, survival probabilities are: FF: 60%, Ff: 60%, ff: 20%. If pollution continues for many generations, what is the most likely trend in allele frequencies?
Answer: Allele F increases because genotypes with at least one F have higher survival than ff
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The DIRECTION of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the RATE depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). In this fish population under pollution, survival probabilities are FF: 60%, Ff: 60%, ff: 20%—notice that any genotype containing at least one F allele (FF and Ff) has 60% survival, while ff has only 20% survival, creating a 40 percentage point advantage for F-containing fish, so F allele frequency will increase over generations. Choice B correctly predicts that allele F increases because genotypes with at least one F have higher survival than ff, leading to more F alleles in the next generation. Choice A incorrectly suggests f increases (but ff has lowest survival!), C wrongly claims no change because FF and Ff are equal (but both are much higher than ff), and D misunderstands that both alleles can't increase simultaneously. Predicting frequency changes from probabilities: (1) IDENTIFY survival probabilities: FF: 60%, Ff: 60%, ff: 20%. (2) COMPARE probabilities: F-containing genotypes (FF, Ff) have 3× higher survival than ff (60% vs 20%). (3) PREDICT direction: Since F appears in high-survival genotypes, F frequency INCREASES. Since ff has low survival, f frequency DECREASES. (4) ASSESS magnitude: LARGE probability difference (40 percentage points) → RAPID frequency change. Real-world example: heavy metal tolerance in plants near mines—if TT and Tt plants survive toxic soil at 70% while tt plants survive at 10%, the T (tolerance) allele rapidly increases, eventually making most plants near the mine tolerant! - A population is close to Hardy-Weinberg equilibrium (allele frequencies stable) for a gene with alleles A and a. Then a new predator arrives. After the predator arrives, survival probabilities become: AA: 90%, Aa: 90%, aa: 20%. What is the most likely change in allele frequencies over the next few generations?
Answer: Allele A will increase because genotypes containing A survive much more often than aa.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability (in both AA and Aa) while aa individuals have only 20% survival probability (HUGE probability difference), then A-carrying individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The population starts at Hardy-Weinberg equilibrium (stable frequencies) but the new predator disrupts this by creating differential survival. Choice B correctly predicts that allele A will increase because genotypes containing A (AA=90%, Aa=90%) survive much more often than aa (20%). Choice A incorrectly claims rare alleles always increase under selection, when actually selection favors alleles that increase survival regardless of rarity; C wrongly invokes Hardy-Weinberg equilibrium which is violated by differential survival; D makes the impossible claim that both alleles will increase when they must sum to 100%. Predicting frequency changes: (1) IDENTIFY survival probabilities: AA: 90%, Aa: 90%, aa: 20%. (2) COMPARE: A-containing genotypes have MUCH HIGHER survival (70 percentage point advantage!). (3) PREDICT: A frequency INCREASES rapidly, a frequency DECREASES rapidly. (4) ASSESS: This 70-point survival difference represents STRONG selection—expect rapid evolution away from equilibrium! - In a fish population, a toxin enters the water. Survival probabilities are: TT: 0.95, Tt: 0.50, tt: 0.05. Which statement best predicts how allele frequencies will change (direction only) after several generations in the toxic water?
Answer: Allele T will increase because genotypes with more T have higher survival probabilities.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. With survival probabilities TT: 0.95, Tt: 0.50, tt: 0.05, we see a clear pattern: more T alleles = higher survival. TT fish have 95% survival, Tt have 50%, and tt have only 5%—showing T provides toxin resistance. Choice C correctly predicts T will increase because genotypes with more T have higher survival probabilities. Choice A makes the common error of thinking low survival means "strongly selected" in a positive way (it's strongly selected AGAINST), while B incorrectly invokes Hardy-Weinberg (which assumes NO selection). Predicting frequency changes: (1) IDENTIFY the pattern: TT (95%) > Tt (50%) > tt (5%)—clear dose effect of T allele. (2) COMPARE: Each T allele improves survival dramatically. (3) PREDICT: T allele → frequency INCREASES rapidly (T-carriers survive much better). t allele → frequency DECREASES rapidly (tt fish mostly die). The 90 percentage point difference between TT and tt survival creates extremely strong selection—T frequency will increase very quickly! - In a population of rabbits, a gene affects coat color. In an environment with dark soil, predators more easily spot light-colored rabbits. Survival probabilities are: dark-coated rabbits 75%, light-coated rabbits 25%. If these survival rates continue, which statement is most accurate about trait frequency changes?
Answer: Dark coat color will increase because dark rabbits have a higher probability of surviving and reproducing.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The DIRECTION of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the RATE depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). Example: if 100 bacteria, 10 resistant (10%) and 90 susceptible (90%), antibiotic kills 95% of susceptible (only ~5 survive) but kills only 10% of resistant (9 survive), then next generation starts with ~5 susceptible + ~9 resistant = ~14 total, with ~64% resistant (9/14)—resistance frequency jumped from 10% to 64% in one generation due to huge survival probability difference! This probability-based frequency change IS evolution by natural selection! Dark-coated rabbits have 75% survival vs 25% for light, so dark ones are three times more likely to reproduce, increasing dark frequency over time. Choice B correctly predicts dark coat color will increase because dark rabbits have higher survival and reproduction probability. Choice A fails by suggesting predators remove dark to 'balance,' but selection increases advantageous traits based on probabilities. Predicting frequency changes from probabilities: (1) IDENTIFY survival: Dark 75%, Light 25%. (2) COMPARE: Dark higher. (3) PREDICT direction: Dark INCREASES, Light DECREASES. (4) ASSESS magnitude: LARGE diff (50 points) → RAPID change. You're hopping ahead—great predictions!
- A rabbit population has two coat colors: white and brown. In a snowy habitat, white rabbits have a 75% chance of surviving to reproduce, while brown rabbits have a 25% chance. If the habitat stays snowy, which outcome is most likely after many generations?
Answer: White coat color becomes more common because white rabbits are more likely to survive and reproduce
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The DIRECTION of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the RATE depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). In this snowy habitat, white rabbits have 75% survival probability while brown rabbits have only 25% survival probability—this 50 percentage point difference means white rabbits contribute three times as many offspring to future generations, causing white coat color frequency to increase over time. Choice C correctly predicts that white coat color becomes more common because white rabbits are more likely to survive and reproduce in the snowy environment. Choice A incorrectly assumes rare traits increase (selection favors beneficial traits regardless of current frequency), B wrongly claims survival doesn't affect reproduction (survivors are the ones who reproduce!), and D misunderstands evolution (individuals can't change their genes—populations evolve through differential survival). Predicting frequency changes from probabilities: (1) IDENTIFY survival probabilities: White coat: 75% survive to reproduce. Brown coat: 25% survive to reproduce. (2) COMPARE probabilities: White rabbits have 3× higher survival (75% vs 25%). (3) PREDICT direction: Higher probability variant (white) → frequency INCREASES. Lower probability variant (brown) → frequency DECREASES. (4) ASSESS magnitude: LARGE probability difference (50 percentage points) → RAPID frequency change. Real-world example: snowshoe hares change from brown in summer to white in winter, but with climate change reducing snow cover, brown hares now survive better during shorter winters, causing evolutionary change in molt timing—probability of survival drives evolution!
- A population of insects has two alleles, H and h, affecting resistance to a pesticide. In Field A (strong selection), survival is: resistant = 90%, non-resistant = 10%. In Field B (weak selection), survival is: resistant = 90%, non-resistant = 85%. In which field will the resistance trait increase in frequency faster, and why?
Answer: Field A, because the survival probability difference between types is much larger (stronger selection).
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: the RATE of evolutionary change depends on the MAGNITUDE of probability differences between variants—LARGE differences create stronger selection and faster evolution, while SMALL differences create weaker selection and slower evolution. In Field A, resistant insects have 90% survival while non-resistant have 10% survival (80 percentage point difference = STRONG selection), whereas in Field B, resistant have 90% survival while non-resistant have 85% survival (only 5 point difference = WEAK selection). Choice B correctly identifies that resistance will increase faster in Field A because the survival probability difference between types is much larger (80 points vs 5 points), creating stronger selection pressure. Choice A incorrectly focuses on overall survival rather than differential survival; C wrongly invokes mutation during lifetime when evolution works through differential survival/reproduction of existing variants; D misses that equal survival of resistant types doesn't determine rate—it's the DIFFERENCE from non-resistant that matters. Comparing selection strengths: Field A: 90% - 10% = 80 point difference = VERY STRONG selection = RAPID evolution. Field B: 90% - 85% = 5 point difference = WEAK selection = SLOW evolution. Real-world application: this explains why pesticide resistance evolves faster with higher pesticide doses (creating larger survival differences) than with lower doses!
- In a rabbit population, fur thickness is influenced by a gene with alleles T (thick) and t (thin). A harsh winter occurs. Survival probabilities are: TT: 85%, Tt: 80%, tt: 75%. Compared with a year with no selection, what is the best prediction about how quickly allele frequencies will change due to this winter?
Answer: Frequencies will change slowly because survival differences among genotypes are small (weak selection).
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies—the RATE of change depends on probability differences: LARGE differences = stronger selection = faster change, SMALL differences = weaker selection = slower change. In this case, survival probabilities are TT: 85%, Tt: 80%, tt: 75%—only 10 percentage points separate highest from lowest survival, indicating WEAK selection. Choice C correctly recognizes that frequencies will change slowly because survival differences among genotypes are small (weak selection). Choice A incorrectly claims rapid change when the survival differences are actually small (85% vs 75% is only 10 points difference); B wrongly states no change will occur when there ARE survival differences; D makes a prediction about direction without addressing the question about rate of change. Predicting rate of change from probabilities: (1) IDENTIFY survival differences: TT (85%) - tt (75%) = 10 percentage points. (2) ASSESS selection strength: 10 point difference = WEAK selection (compare to strong selection like 90% vs 10% = 80 points!). (3) PREDICT rate: SLOW frequency change over many generations. Real-world context: this weak selection is common in nature—most traits don't face life-or-death differences but small advantages that accumulate slowly over time. Evolution can be gradual when selection is weak!
- A plant trait (waxy leaves) helps reduce water loss. In a drought year, plants with waxy leaves produce an average of 30 seeds each, while plants without waxy leaves produce an average of 10 seeds each. If conditions stay similar for multiple generations, what is the most likely change in the frequency of the waxy-leaf trait?
Answer: It will increase because individuals with the trait contribute more offspring to the next generation.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The DIRECTION of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the RATE depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). Example: if 100 bacteria, 10 resistant (10%) and 90 susceptible (90%), antibiotic kills 95% of susceptible (only ~5 survive) but kills only 10% of resistant (9 survive), then next generation starts with ~5 susceptible + ~9 resistant = ~14 total, with ~64% resistant (9/14)—resistance frequency jumped from 10% to 64% in one generation due to huge survival probability difference! This probability-based frequency change IS evolution by natural selection! For these plants, waxy leaves lead to 30 seeds vs 10 for non-waxy, so waxy plants contribute three times more offspring, increasing the trait's frequency over generations. Choice B correctly predicts it will increase because individuals with the trait contribute more offspring to the next generation. Choice A fails by assuming more seeds reduce long-term survival, but the data shows higher reproduction directly increases frequency. Predicting frequency changes from probabilities: (1) IDENTIFY reproduction: Waxy: 30 seeds, Non-waxy: 10. (2) COMPARE: Waxy much higher. (3) PREDICT direction: Waxy frequency INCREASES. (4) ASSESS magnitude: LARGE difference (3x) → RAPID change. You're building strong skills here—keep it up!
- In a bacterial population, 10% of cells carry a resistance allele R and 90% are susceptible (r). After an antibiotic treatment, 95% of susceptible cells die, but only 5% of resistant cells die. Without doing exact calculations, what will happen to the frequency of the resistance allele R among the surviving bacteria?
Answer: It will increase because resistant cells have a much higher probability of surviving the antibiotic.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. In this bacterial population, resistant cells (R) have 95% survival (only 5% die) while susceptible cells (r) have only 5% survival (95% die)—a HUGE 90 percentage point difference! This means R cells contribute vastly more to the surviving population, causing R frequency to skyrocket. Choice C correctly predicts frequency changes by recognizing the much higher survival probability of resistant cells leads to increasing R frequency. Choice A incorrectly focuses on initial frequencies rather than survival differences, while B wrongly claims antibiotics don't affect allele frequencies (they do through differential survival!). Predicting frequency changes: Initially 10% R, 90% r. After antibiotic: R cells: 95% survive (almost all live). r cells: 5% survive (almost all die). The surviving population is now dominated by R cells! Example calculation: From 100 bacteria (10 R, 90 r), after treatment: ~9.5 R survive, ~4.5 r survive. New R frequency = 9.5/(9.5+4.5) = 68%! The resistance frequency jumped from 10% to 68% in one generation due to extreme survival probability difference!
- In a fish species, tolerance to polluted water is influenced by a gene with alleles P (tolerant) and p (not tolerant). In polluted water, survival probabilities are: PP: 85%, Pp: 80%, pp: 15%. If the river stays polluted for many generations, what is the most likely long-term trend?
Answer: Allele P will increase because PP and Pp are much more likely to survive and reproduce than pp.
This question tests your ability to use probability and differential survival/reproduction data to predict how trait and allele frequencies change in populations over time through natural selection. Probability reasoning for evolution: when different variants have different survival or reproduction probabilities, this creates PREDICTABLE changes in allele frequencies: if individuals with allele A have 90% survival probability while individuals with allele a have 30% survival probability (large probability difference), then A individuals contribute disproportionately more offspring to next generation, causing A allele frequency to INCREASE and a allele frequency to DECREASE. The DIRECTION of change is predictable (higher survival/reproduction → increase frequency, lower survival/reproduction → decrease frequency), and the RATE depends on probability differences (larger differences = stronger selection = faster change, smaller differences = weaker selection = slower change). Example: if 100 bacteria, 10 resistant (10%) and 90 susceptible (90%), antibiotic kills 95% of susceptible (only ~5 survive) but kills only 10% of resistant (9 survive), then next generation starts with ~5 susceptible + ~9 resistant = ~14 total, with ~64% resistant (9/14)—resistance frequency jumped from 10% to 64% in one generation due to huge survival probability difference! This probability-based frequency change IS evolution by natural selection! In polluted water, PP (85%) and Pp (80%) far out-survive pp (15%), so P frequency will increase over generations as tolerant genotypes contribute more. Choice B correctly predicts allele P will increase because PP and Pp are much more likely to survive and reproduce than pp. Choice A fails by claiming low survival leads to more reproduction to 'replace losses,' but actually, lower survival means fewer offspring contributed. Predicting frequency changes from probabilities: (1) IDENTIFY survival: PP 85%, Pp 80%, pp 15%. (2) COMPARE: More P = higher survival. (3) PREDICT direction: P INCREASES, p DECREASES. (4) ASSESS magnitude: LARGE diff (70 points) → RAPID change. Fantastic work—you're mastering selection!
