Biology Quiz: Use Probability For Trait Frequency

What this quiz covers

This quiz focuses on Use Probability For Trait Frequency, giving you a quick way to practice the rules, question types, and explanations that matter most for Biology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Brown coat color becomes more common because it is currently less common
2. Coat color frequencies do not change because survival is not related to reproduction
3. White coat color becomes more common because white rabbits are more likely to survive and reproduce (correct answer)
4. Individual brown rabbits will turn white during winter, increasing white frequency without selection

Explanation: 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!

Question 2

1. Allele $B$ decreases because $Bb$ has lower survival than $BB$
2. Allele $B$ increases because genotypes with $B$ (especially $BB$) survive much more often than $bb$ (correct answer)
3. Allele $B$ stays the same because selection affects individuals, not allele frequencies
4. Allele $B$ increases only if the toxin causes new mutations to create more $B$ alleles

Explanation: 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 insect population exposed to toxin, survival probabilities are BB: 85%, Bb: 40%, bb: 10%—while Bb has intermediate survival, BB has much higher survival than both other genotypes, and overall, B-containing genotypes survive better than bb, so B allele frequency will increase over time. Choice B correctly predicts that allele B increases because genotypes with B (especially BB at 85%) survive much more often than bb (only 10%), even though Bb is intermediate. Choice A incorrectly focuses only on Bb being lower than BB (missing that both are higher than bb), C wrongly claims selection doesn't affect allele frequencies, and D incorrectly requires new mutations rather than selection on existing variation. Predicting frequency changes from probabilities: (1) IDENTIFY survival probabilities: BB: 85%, Bb: 40%, bb: 10%. (2) ANALYZE allele representation: B appears in BB (85% survival) and Bb (40% survival). b appears in Bb (40% survival) and bb (10% survival). (3) CALCULATE weighted average: B allele "sees" average survival of ~62.5% (averaging BB and Bb). b allele "sees" average survival of ~25% (averaging Bb and bb). (4) PREDICT: B has higher average survival → B frequency INCREASES. This shows even with heterozygote disadvantage (Bb lower than both homozygotes), B still increases because BB survival is so high! Real-world example: sickle cell and malaria—even though sickle cell heterozygotes have some health issues, the allele persists in malaria regions because homozygotes for normal hemoglobin die from malaria at high rates!

Question 3

1. Allele frequencies will change faster in the dry year because both genotypes have high survival
2. Allele frequencies will change at the same rate in both situations because selection is always equally strong
3. Allele frequencies will change more slowly in the dry year because the survival difference (92% vs 88%) is small (weak selection) (correct answer)
4. Allele frequencies will not change at all in the dry year because any difference under 10% cannot cause evolution

Explanation: 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). This question compares two selection scenarios: in the dry year, AA survives at 92% and aa at 88% (only 4 percentage point difference), while the comparison scenario has AA at 92% and aa at 12% (80 percentage point difference)—the tiny 4-point difference in the dry year means WEAK selection and SLOW frequency change, while the huge 80-point difference means STRONG selection and RAPID change. Choice C correctly recognizes that allele frequencies will change more slowly in the dry year because the survival difference (92% vs 88%) is small, indicating weak selection. Choice A gets it backwards (small differences = slow change, not fast), B incorrectly claims selection is always equally strong, and D wrongly suggests no evolution occurs with small differences (evolution still happens, just slowly). Predicting frequency changes from probabilities: (1) IDENTIFY survival differences: Dry year: 92% - 88% = 4 percentage points. Comparison: 92% - 12% = 80 percentage points. (2) COMPARE selection strength: 4-point difference = WEAK selection. 80-point difference = STRONG selection. (3) PREDICT rate: Weak selection → SLOW frequency change (many generations for noticeable change). Strong selection → RAPID frequency change (big changes in few generations). (4) Both cause evolution, but at very different speeds! Real-world example: antibiotic resistance with different drugs—if Drug A kills 99% of susceptible bacteria but 1% of resistant (98-point difference), resistance evolves FAST. If Drug B kills 55% of susceptible but 50% of resistant (5-point difference), resistance still evolves but MUCH more slowly!

Question 4

1. Resistance frequency increases because resistant cells have a much higher survival probability (correct answer)
2. Resistance frequency decreases because most bacteria were susceptible to begin with
3. Resistance frequency stays the same because antibiotics do not affect allele frequencies
4. Resistance frequency changes randomly with no predictable direction

Explanation: 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 resistant bacteria have 95% survival while susceptible have 5% (huge probability difference), then resistant individuals contribute disproportionately more to the next generation, causing resistance frequency to increase dramatically. 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 bacterial population, starting with 10% resistant, the antibiotic creates a massive survival difference (95% resistant survive vs 5% susceptible), so the surviving population will have a much higher proportion of resistant cells, increasing the resistance frequency. Choice A correctly predicts that resistance frequency increases because resistant cells have a much higher survival probability, directly linking the probability gap to the frequency shift. Choice B fails by suggesting resistance decreases due to initial majority of susceptible cells, overlooking how differential survival disproportionately favors resistant ones. Predicting frequency changes from probabilities: (1) Identify survival probabilities: resistant 95%, susceptible 5%. (2) Compare: resistant much higher. (3) Predict direction: resistance increases. (4) Assess magnitude: Huge difference (90 percentage points) means rapid change, like in the example where resistance jumps from 10% to about 68% in one generation! This is why antibiotic resistance evolves so quickly in real-world bacterial populations under treatment.

Question 5

1. No change, because the survival differences are small so selection cannot act.
2. A rapid increase in $F$ frequency, because any survival advantage causes immediate fixation.
3. A slow increase in $F$ frequency, because $F$-containing genotypes survive slightly more often. (correct answer)
4. A slow increase in $f$ frequency, because weaker selection favors the recessive allele.

Explanation: 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 colder climate, the small survival edges (FF 55%, Ff 50%, ff 45%) mean F-carrying mice slightly out-survive ff, leading to a gradual increase in F frequency over many generations, not instantly. Choice C correctly predicts a slow increase in F by noting the slight survival advantage translates to weak selection and gradual change. Choice B fails by overestimating small differences as causing rapid fixation, but actually, tiny gaps (like 5-10 percentage points) result in slow evolution—keep practicing, you're getting it! Strategy tip: (1) IDENTIFY: FF 55%, Ff 50%, ff 45%; (2) COMPARE: F slightly higher; (3) PREDICT: F increases slowly; (4) ASSESS: small differences = weak selection, like a 10% reproduction boost leading to slow change over time.

Question 6

1. They will stay approximately constant because no selection (or other forces) is acting (correct answer)
2. They will always shift toward whichever allele is rarer
3. They will change because evolution happens every generation no matter what
4. They will change only if individual lizards choose mates with the same genotype

Explanation: 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!

Question 7

1. It increases because resistant bacteria have a much higher survival probability (correct answer)
2. It decreases because most bacteria die, so resistance becomes less common
3. It stays the same because antibiotics do not affect allele frequencies
4. It changes randomly with no predictable direction because survival is unrelated to resistance

Explanation: 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 bacterial population, we start with 10% resistant and 90% susceptible, but antibiotic treatment creates HUGE survival differences: resistant bacteria have 95% survival (only 5% die) while susceptible bacteria have only 5% survival (95% die)—this massive 90 percentage point difference means resistant bacteria dominate among survivors, causing resistant frequency to skyrocket! Choice A correctly predicts that resistance frequency increases because resistant bacteria have much higher survival probability during antibiotic treatment. Choice B incorrectly assumes resistance decreases just because many bacteria die (but resistant ones survive much better!), while C and D wrongly claim antibiotics don't affect frequencies or that changes are random. Predicting frequency changes from probabilities: (1) IDENTIFY survival probabilities: Resistant: 95% survive (5% die). Susceptible: 5% survive (95% die). (2) COMPARE probabilities: Resistant bacteria have 19× higher survival rate! (95% vs 5%). (3) PREDICT direction: Higher probability variant (resistant) → frequency INCREASES dramatically. Lower probability variant (susceptible) → frequency DECREASES dramatically. (4) ASSESS magnitude: EXTREME probability difference (90 percentage points) → VERY RAPID frequency change. Example calculation: if we start with 100 bacteria (10 resistant, 90 susceptible), after treatment we have ~9.5 resistant survivors and ~4.5 susceptible survivors, so resistance jumps from 10% to ~68% (9.5/14) in just one generation! This is why antibiotic resistance spreads so fast—extreme selection pressure creates rapid evolution!

Question 8

1. Allele $g$ increases because rare alleles are always favored by selection
2. Allele $G$ increases because genotypes with $G$ have higher survival probabilities (correct answer)
3. Neither allele changes because survival is based on chance, not genetics
4. Both alleles increase because more beetles survive overall

Explanation: 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 beetle population, we see survival probabilities of GG: 90%, Gg: 80%, gg: 20%—notice that genotypes containing allele G have much higher survival (90% and 80%) compared to gg (only 20%), so G-containing beetles contribute more offspring to the next generation, causing allele G frequency to increase. Choice B correctly predicts frequency changes by recognizing that genotypes with G have higher survival probabilities, leading to G increasing in frequency. Choice A incorrectly claims rare alleles are favored (not true—selection favors beneficial alleles regardless of rarity), while C wrongly suggests genetics doesn't matter, and D misunderstands that both alleles can't increase (frequencies must sum to 100%). Predicting frequency changes from probabilities: (1) IDENTIFY survival probabilities for each genotype: GG: 90%, Gg: 80%, gg: 20%. (2) COMPARE probabilities: Which genotypes survive better? (GG and Gg both have much higher survival than gg). (3) PREDICT direction: Since G appears in the high-survival genotypes (GG and Gg), allele G frequency INCREASES. Since gg has low survival, allele g frequency DECREASES. (4) ASSESS magnitude: LARGE probability difference (90%/80% vs 20% = 60-70 percentage point difference) → RAPID frequency change (strong selection). Real-world example: insecticide resistance works exactly like this—if RR insects have 95% survival, Rr have 85% survival, and rr have 5% survival when sprayed, the R allele rapidly increases because R-containing genotypes survive at much higher rates!

Question 9

1. It will decrease because most bacteria were susceptible before treatment.
2. It will stay the same because antibiotics do not affect allele frequencies, only population size.
3. It will increase because resistant cells have a much higher probability of surviving the antibiotic. (correct answer)
4. It will change randomly because survival is not related to genotype in this scenario.

Explanation: 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!

Question 10

1. The waxy-leaf trait becomes more common because those plants contribute more offspring (correct answer)
2. The waxy-leaf trait becomes less common because producing more seeds uses too much energy
3. The waxy-leaf trait stays the same because reproduction differences do not affect frequencies
4. The waxy-leaf trait appears in all plants within one generation because selection changes individuals

Explanation: 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 waxy-leaf plants produce 2x as many seeds (100% higher reproduction), then they contribute disproportionately more offspring, causing waxy-leaf frequency to increase. 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 plant population, waxy-leaf individuals have double the seed production, meaning they are twice as likely to pass on their traits, so over many generations, the waxy-leaf trait will become more common as it spreads through the population. Choice A correctly predicts the waxy-leaf trait becomes more common because those plants contribute more offspring, tying reproduction differences to frequency increase. Choice B fails by suggesting it becomes less common due to energy costs, which isn't supported by the given data on higher reproduction. Predicting frequency changes from probabilities: (1) Identify reproduction rates: waxy 2x, non-waxy 1x. (2) Compare: waxy higher. (3) Predict direction: waxy increases. (4) Assess magnitude: 100% difference means strong selection and fast change, like how drought-resistant crops evolve quickly under selection in agriculture!

Question 11

1. Frequencies change more slowly on Island 2 because survival is higher for $TT$
2. Frequencies change at the same rate on both islands because $TT$ survival is 95% on both
3. Frequencies change more quickly on Island 2 because the survival difference between genotypes is much larger (correct answer)
4. Frequencies cannot change on Island 2 because natural selection only affects phenotypes, not genotypes

Explanation: 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: larger differences (e.g., 95% vs 15%) lead to faster changes than smaller ones (95% vs 90%), as the favored variant contributes much more disproportionately. 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). On Island 2, the survival gap (95% TT vs 15% tt) is much larger than on Island 1 (95% vs 90%), so TT frequency will increase much more quickly on Island 2 due to stronger selection pressure. Choice C correctly predicts frequencies change more quickly on Island 2 because the survival difference between genotypes is much larger, emphasizing the role of probability gaps in selection strength. Choice A fails by reversing this, claiming slower change on Island 2 despite the larger difference. Predicting frequency changes from probabilities: (1) Identify and compare survival on each island. (2) Compare differences: Island 2 has 80-point gap vs Island 1's 5-point. (3) Predict: Both favor TT, but Island 2 faster. (4) Assess magnitude: Larger gap = stronger, faster evolution, like rapid adaptation in extreme environments such as Galapagos finches during droughts!

Question 12

1. Striped fish become more common because they have a higher probability of surviving to reproduce (correct answer)
2. Striped fish become less common because predators will focus on them
3. Striped fish frequency stays the same because survival does not affect reproduction
4. Striped fish frequency changes randomly because selection cannot be predicted from probabilities

Explanation: 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!

Question 13

1. Allele $d$ increases because $Dd$ has intermediate survival
2. Allele $D$ increases because genotypes with more $D$ have higher survival (correct answer)
3. No allele changes because predation is a random event
4. Both alleles increase because $DD$ survival is high

Explanation: 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: higher survival for DD (85%) and Dd (50%) vs dd (15%) means D alleles are more likely to be passed on, increasing D 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 this mouse population, predation favors darker fur (associated with D), with stepped survival probabilities showing genotypes with more D alleles surviving better, so over generations, D frequency will increase as it becomes more common. Choice B correctly predicts allele D increases because genotypes with more D have higher survival, linking the probability gradient to frequency change. Choice A fails by claiming d increases due to intermediate Dd survival, misinterpreting the overall advantage for D. Predicting frequency changes from probabilities: (1) Identify survival: DD 85%, Dd 50%, dd 15%. (2) Compare: More D = higher survival. (3) Predict direction: D increases, d decreases. (4) Assess magnitude: Large differences (70 points max) mean strong selection, like camouflage evolution in pocket mice on dark lava rocks!

Question 14

1. Allele frequencies should begin to change because selection has been introduced (correct answer)
2. Allele frequencies should remain constant because Hardy-Weinberg always holds once reached
3. Only individual genotypes change; population allele frequencies do not change
4. The $b$ allele must increase because it is now rare

Explanation: 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: introducing lower survival for bb (much lower than BB/Bb) disrupts equilibrium, causing b frequency to decrease as bb contribute fewer offspring. 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). After pollution introduces selection against bb, the population deviates from Hardy-Weinberg as bb's lower survival means fewer b alleles are passed on, so allele frequencies will change with B increasing and b decreasing. Choice A correctly predicts that allele frequencies should begin to change because selection has been introduced, recognizing how differential survival drives evolution. Choice B fails by insisting Hardy-Weinberg always holds, ignoring that selection violates its assumptions. Predicting frequency changes from probabilities: (1) Identify new survival: bb much lower. (2) Compare: BB/Bb higher. (3) Predict direction: B increases, b decreases. (4) Assess magnitude: Large difference means noticeable change, like how industrial pollution drove frequency shifts in moth populations!

Question 15

1. The $R$ allele frequency will decrease because resistant insects survive and therefore face more competition
2. The $R$ allele frequency will increase because insects with at least one $R$ allele survive more often (correct answer)
3. The $R$ allele frequency will not change because pesticides cause death, not evolution
4. The $R$ allele frequency will increase only if new $R$ mutations occur; survival differences do not matter

Explanation: 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: RR (90%) and Rr (70%) much higher than rr (10%) means R alleles are favored, increasing R frequency as resistant insects reproduce more. 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). Continued pesticide use will select for resistance, with genotypes carrying R having higher survival, so the R allele will become more common over generations. Choice B correctly predicts the R allele frequency will increase because insects with at least one R allele survive more often, accurately tying probabilities to evolution. Choice A fails by claiming R decreases due to competition, ignoring how survival advantages drive frequency up. Predicting frequency changes from probabilities: (1) Identify survival: RR 90%, Rr 70%, rr 10%. (2) Compare: R-carriers higher. (3) Predict direction: R increases. (4) Assess magnitude: Large differences (80 points max) mean rapid change, like how insecticide resistance evolves quickly in pest populations worldwide!

Question 16

1. Island 2 will change faster because survival is higher overall.
2. Island 1 will change faster because the survival differences between genotypes are much larger. (correct answer)
3. Both islands will change at the same rate because selection always changes allele frequencies equally.
4. Neither island will change because Hardy-Weinberg equilibrium prevents selection from acting.

Explanation: 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). Island 1 has massive survival gaps (95% vs 10%), creating strong selection for H, while Island 2's tiny differences (95% vs 90%) mean weak selection, so frequencies change much faster on Island 1. Choice B correctly compares that Island 1 changes faster due to larger probability differences driving stronger selection. Choice A fails by focusing on overall survival instead of differences between genotypes, but it's the gap that determines selection strength—excellent insight! Use this: (1) IDENTIFY per island; (2) COMPARE gaps: Island 1 huge, Island 2 small; (3) PREDICT: faster on Island 1; (4) ASSESS: like extreme vs mild antibiotic pressure, where bigger differences speed evolution.

Question 17

1. Purple will become more common because higher reproduction probability increases its contribution to the next generation. (correct answer)
2. White will become more common because producing fewer seeds reduces competition.
3. Trait frequencies will not change unless the population is not in Hardy-Weinberg equilibrium.
4. Trait frequencies will change randomly because reproduction is not related to evolution.

Explanation: 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). Purple plants producing twice as many seeds means they have double the reproduction probability, so they contribute far more offspring, predictably increasing purple trait frequency over generations. Choice A correctly states purple will become more common by linking higher reproduction to greater generational contribution. Choice B fails by suggesting fewer seeds help white via reduced competition, but actually, lower reproduction decreases frequency—nice try, but reproduction drives selection here! Remember: (1) IDENTIFY reproduction rates: purple 2x white; (2) COMPARE: purple higher; (3) PREDICT: purple increases; (4) ASSESS: doubling is a large difference, like strong selection causing fast change, similar to antibiotic examples.

Question 18

1. Allele frequencies will remain constant because Hardy-Weinberg equilibrium always holds.
2. The $t$ allele frequency will increase because predators remove the most common genotype.
3. The $T$ allele frequency will increase because individuals with $T$ have higher survival probabilities. (correct answer)
4. Allele frequencies will change only if new mutations occur; survival differences do not matter.

Explanation: 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). The new predator disrupts Hardy-Weinberg equilibrium by creating survival differences (TT 80%, Tt 60%, tt 30%), so birds with more T alleles are more likely to survive and reproduce, predictably increasing T's frequency over generations. Choice C correctly identifies that T will increase due to its link to higher survival probabilities in T-containing genotypes. Choice A fails by assuming HWE always holds, but HWE requires no selection, and here selection is acting—great job spotting that violation! Use this strategy: (1) IDENTIFY probabilities: TT 80%, Tt 60%, tt 30%; (2) COMPARE: T associated with higher survival; (3) PREDICT: T increases; (4) ASSESS: moderate differences suggest steady change, unlike weak selection where it's slower.

Question 19

1. Allele $S$ will increase because $SS$ individuals are being selected for.
2. Allele $s$ will increase because genotypes with more $s$ alleles have higher survival probabilities. (correct answer)
3. Neither allele will change because pollution only changes survival, not allele frequencies.
4. Both alleles will increase because heterozygotes survive at an intermediate rate.

Explanation: 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). With pollutant survival at SS 20%, Ss 60%, ss 80%, genotypes with more s alleles have higher probabilities, so s-carrying fish disproportionately survive and reproduce, increasing s frequency. Choice B correctly predicts s will increase by recognizing its association with higher survival in s-containing genotypes. Choice A fails by saying S increases due to SS selection, but SS has the lowest survival, so direction is opposite—keep going, you're learning fast! Strategy: (1) IDENTIFY: SS 20%, Ss 60%, ss 80%; (2) COMPARE: s linked to higher; (3) PREDICT: s increases; (4) ASSESS: large gaps (80% vs 20%) mean rapid change, like resistance evolving quickly under strong pressure.

Question 20

1. It increases because R has a much higher probability of survival than S. (correct answer)
2. It decreases because antibiotics cause bacteria to become susceptible.
3. It stays the same because selection cannot change frequencies in one generation.
4. It changes randomly with no predictable direction because survival is based on chance alone.

Explanation: 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.