Continuing Evolution
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AP Biology › Continuing Evolution
In a city park, a population of pigeons includes two alleles at a gene affecting beak depth: D (deeper) and d (shallower). After a shift in available food toward larger, harder seeds, researchers sample allele frequencies each breeding season for 5 seasons. Allele D increases from 0.33 to 0.58. Which observation best demonstrates continuing evolution in the pigeon population?
Individual pigeons developed stronger jaw muscles after eating harder seeds for several weeks.
The average seed size in the park increased when a new tree species was planted.
Some pigeons switched from seeds to insects during summer when insects were abundant.
Pigeons spent more time foraging near benches where visitors dropped food scraps.
Allele D increased from 0.33 to 0.58 across five breeding seasons in the park population.
Explanation
Continuing evolution refers to genetic shifts in populations adapting to new conditions, such as these pigeons facing harder seeds. The correct answer, choice B, demonstrates this as allele D for deeper beaks rose from 0.33 to 0.58 over five breeding seasons, implying better food handling led to higher survival and reproduction. This population trend reflects natural selection favoring deeper beaks in the changed food environment. Consistent sampling across seasons highlights the heritable nature of the change. Choice A tempts with muscle development from eating harder seeds, a misconception of acquired traits or plasticity rather than genetic evolution. A transferable approach is to examine allele frequency data over generations to confirm evolution, avoiding confusion with non-heritable changes.
A population of rabbits includes two alleles at a coat-color locus: W (white) and B (brown). In 2017, snow cover duration decreased due to warmer winters. Researchers sampled the same population each spring: 2016 $f(B)=0.12$, 2018 $f(B)=0.20$, 2020 $f(B)=0.29$, 2022 $f(B)=0.33$. Predators more easily detect white coats on snow-free ground. Which observation best demonstrates continuing evolution in this rabbit population?
More predators are observed hunting in open areas during low-snow winters.
Juvenile rabbits grow more slowly when winter temperatures are above average.
Some rabbits change hiding behavior by using shrubs more on snow-free days.
Individual rabbits shed fur earlier in warm years than in cold years.
The frequency of allele B increases in the population over successive years.
Explanation
This question assesses the skill of understanding continuing evolution, which involves ongoing changes in allele frequencies within a population over generations due to selective pressures. The correct answer, choice B, demonstrates evolution because it shows the frequency of the B allele increasing from 0.12 in 2016 to 0.20 in 2018, 0.29 in 2020, and 0.33 in 2022, indicating a population trend toward brown coats as snow cover decreases. This change reflects natural selection favoring brown rabbits that are less detectable by predators on snow-free ground, enhancing survival and reproduction. Spring sampling of the same population tracks the genetic response to warmer winters. A tempting distractor is choice A, which describes individual rabbits shedding fur earlier in warm years, but this is wrong because it represents seasonal phenotypic plasticity, not genetic evolution across generations. To identify evidence of continuing evolution in similar questions, focus on data showing shifts in allele or genotype frequencies over multiple generations rather than short-term individual responses.
A population of field mice includes two hemoglobin alleles, H1 and H2. In 2000, $f(H2)=0.10$ in a lowland population. A drought from 2001–2004 reduced available water, and the same population was sampled each year: 2002 $f(H2)=0.16$, 2004 $f(H2)=0.23$, 2006 $f(H2)=0.24$. H2 is associated with improved oxygen delivery during dehydration stress. Which observation best demonstrates evolution occurring in this mouse population?
Some mice migrate from nearby hills into the lowlands during the drought.
The population’s allele frequency for H2 increases across multiple sampling years.
Young mice weigh less at weaning during the driest years of the study.
Mice increase burrow use during hot days to reduce water loss.
Individual mice drink less water during drought years than during wetter years.
Explanation
This question assesses the skill of understanding continuing evolution, which involves ongoing changes in allele frequencies within a population over generations due to selective pressures. The correct answer, choice B, demonstrates evolution because it shows the frequency of the H2 allele increasing from 0.10 in 2000 to 0.16 in 2002, 0.23 in 2004, and 0.24 in 2006, indicating a population trend toward better oxygen delivery during drought stress. This shift reflects natural selection favoring mice with the H2 allele that cope better with dehydration, resulting in higher survival and reproductive success. The consistent sampling during and after the drought period highlights how environmental pressure drives genetic change in the population. A tempting distractor is choice A, which describes individual mice drinking less during droughts, but this is wrong because it represents behavioral adaptation or physiological response within a lifetime, not heritable genetic evolution. To identify evidence of continuing evolution in similar questions, focus on data showing shifts in allele or genotype frequencies over multiple generations rather than short-term individual responses.
A population of mosquitoes is exposed to insecticide-treated bed nets starting in 2011. A sodium-channel allele (kdr) confers reduced sensitivity to the insecticide. In 2011, $f(kdr)=0.08$ in the village population; in 2013, $f(kdr)=0.21$; in 2016, $f(kdr)=0.39$; in 2020, $f(kdr)=0.52$. Mosquitoes were sampled from the same set of households each year. Which observation best demonstrates continuing evolution in this mosquito population?
Some adult mosquitoes live longer when provided sugar water in laboratory cages.
More mosquitoes are captured during the rainy season than during the dry season.
The frequency of the kdr allele increases over years in the village population.
Individual mosquitoes avoid entering houses with bed nets during a single night.
Mosquito larvae develop faster in warmer puddles than in cooler puddles.
Explanation
This question assesses the skill of understanding continuing evolution, which involves ongoing changes in allele frequencies within a population over generations due to selective pressures. The correct answer, choice B, demonstrates evolution because it shows the frequency of the kdr allele increasing from 0.08 in 2011 to 0.21 in 2013, 0.39 in 2016, and 0.52 in 2020, indicating a population trend toward insecticide resistance with bed net use. This change reflects natural selection favoring mosquitoes with reduced sensitivity, allowing better survival and reproduction despite exposure. Consistent sampling from the same households tracks the genetic adaptation over time. A tempting distractor is choice A, which describes individual mosquitoes avoiding houses with nets, but this is wrong because it represents behavioral avoidance or learning, not a heritable shift in allele frequencies. To identify evidence of continuing evolution in similar questions, focus on data showing shifts in allele or genotype frequencies over multiple generations rather than short-term individual responses.
A population of wild sunflowers grows along roadsides where de-icing salt is applied each winter. Salt-tolerance is associated with allele T at a transporter gene. Researchers sampled plants from the same 2 km stretch of road: in 2012, $f(T)=0.14$; in 2015, $f(T)=0.26$; in 2018, $f(T)=0.37$; in 2021, $f(T)=0.40$. Plants with allele T produce more seeds in salty soils than plants without T. Which observation best demonstrates evolution in this sunflower population?
The frequency of allele T increases across years in the roadside population.
Road salt application varies between winters depending on snowfall amounts.
Seedlings grow more slowly when transplanted from the roadside into a greenhouse.
Some plants grow taller in shaded patches than in sunny patches along the road.
Individual sunflowers wilt less on salty days because their leaves close stomata.
Explanation
This question assesses the skill of understanding continuing evolution, which involves ongoing changes in allele frequencies within a population over generations due to selective pressures. The correct answer, choice B, demonstrates evolution because it shows the frequency of the T allele increasing from 0.14 in 2012 to 0.26 in 2015, 0.37 in 2018, and 0.40 in 2021, indicating a population trend toward salt tolerance along salted roadsides. This shift reflects natural selection favoring plants with the T allele that produce more seeds in salty soils, enhancing reproductive success. Sampling from the same road stretch ensures the trend is a genetic response to de-icing salt. A tempting distractor is choice A, which describes individual sunflowers wilting less by closing stomata, but this is wrong because it represents physiological acclimation, not heritable genetic change. To identify evidence of continuing evolution in similar questions, focus on data showing shifts in allele or genotype frequencies over multiple generations rather than short-term individual responses.
A population of yeast is grown in identical flasks, with one sugar source as the only carbon supply. At a gene influencing sugar transport, allele S is initially at frequency 0.50. After 300 generations, allele S is at 0.93 in the same continuously reproducing population. Which observation best demonstrates evolution occurring in this yeast population?
Individual yeast cells increased transporter activity when placed into the sugar medium.
Some yeast cells entered a dormant state when nutrients became temporarily limited in the flask.
Cells clustered together, reducing exposure to ethanol produced during fermentation.
The culture’s growth rate changed when the incubator temperature varied slightly between days.
Allele S increased in frequency from 0.50 to 0.93 over 300 generations in the population.
Explanation
Continuing evolution illustrates genetic changes in lab populations under controlled conditions, as with this yeast in sugar medium. Choice A correctly demonstrates evolution through allele S's rise from 0.50 to 0.93 over 300 generations, indicating better sugar transport conferred advantages, increasing reproduction and shifting population genetics. Identical flasks and continuous reproduction highlight selection's role in this trend. The generational scale confirms a heritable adaptation. Choice B tempts by noting increased transporter activity upon exposure, a misconception of induced physiological changes mistaken for evolution without genetic frequency shifts. A useful strategy is to analyze long-term allele data to verify evolution, separating it from immediate cellular responses.
In a desert annual plant population, two alleles at a flowering-time locus occur: F (earlier flowering) and f (later flowering). After several years of shorter spring rains, researchers sample seeds each generation. Over 6 generations, allele F increases from 0.27 to 0.63, with similar population sizes and no new seed introductions. Which observation best demonstrates continuing evolution in this plant population?
Individual plants flowered earlier when temperatures were warmer during a particular spring.
Plants in drier years produced fewer flowers per individual because water limited growth.
Pollinators visited more frequently during mornings than afternoons in the hottest months.
Seeds germinated later in some years because rainfall occurred later than average.
Allele F increased from 0.27 to 0.63 across six generations in the population.
Explanation
Continuing evolution involves populations genetically adapting to climate variability, like these desert plants with shorter springs. Choice B is correct as allele F for earlier flowering increased from 0.27 to 0.63 over six generations, suggesting earlier bloomers reproduced more successfully before rains ended, altering the population's genetics. Similar population sizes and no seed introductions point to natural selection favoring this trait. The multi-generation trend reflects ongoing heritable changes. Choice C tempts with earlier flowering from warmer temperatures, confusing environmental cues and plasticity with evolutionary genetic shifts. To recognize evolution, focus on tracking allele frequencies over generations, distinguishing from phenotypic responses to conditions.
A population of field mice includes two alleles at a coat-color gene: L (light) and D (dark). After a new predator arrives, biologists sample the population every 2 years. Over 10 years, allele D increases from 0.22 to 0.55, while the habitat and migration rates remain similar. Which observation best demonstrates evolution occurring in this mouse population?
Mice hid under denser vegetation more often after the predator arrived, reducing daytime activity.
Individual mice learned to freeze longer when they detected predator scent near their burrows.
Some mice grew thicker fur during colder winters and thinner fur during warmer winters.
The predator population increased in the first year and then stabilized at a similar density.
Allele D rose in frequency from 0.22 to 0.55 across multiple sampling intervals.
Explanation
Continuing evolution describes genetic adaptations in populations facing new selective pressures, like these field mice with a new predator. The correct answer, choice C, illustrates this through allele D's increase from 0.22 to 0.55 over 10 years, implying darker coats offered camouflage advantages, leading to higher survival and reproduction rates. Consistent habitat and migration rates indicate natural selection drove this population-level genetic shift. The decadal trend reflects ongoing heritable changes in response to predation. Choice A is a tempting distractor, portraying behavioral hiding as evolution, but this misconceptions confuses learned or plastic behaviors with genetic evolution requiring allele changes. To spot evolution, always verify shifts in genetic frequencies over generations, not just behavioral modifications.
In a freshwater lake, a population of snails has two alleles at a shell-thickness locus: T (thick) and t (thin). After an invasive crab appears, researchers track allele frequencies for 7 generations. The frequency of allele T increases from 0.40 to 0.79, and the snail population continues reproducing in the lake with no stocking. Which observation best demonstrates ongoing evolution in this snail population?
Crabs preferred shallow water, causing snails to shift deeper during hot months.
Snails spent more time under rocks during the day when crabs were most active.
Individual snails produced thicker shells when calcium levels were higher in the water.
Some snails repaired shell damage faster after crab attacks during a single growing season.
Allele T increased in frequency from 0.40 to 0.79 across seven generations in the lake.
Explanation
Continuing evolution highlights genetic changes in populations over generations, evident in these snails adapting to an invasive crab. Choice B is correct as allele T for thicker shells rose from 0.40 to 0.79 over seven generations, suggesting snails with thicker shells survived crab predation better and reproduced more, altering the population's genetics. The lack of stocking and continued reproduction in the lake point to natural selection favoring this trait. This generational trend demonstrates heritable adaptations spreading through the population. Choice E tempts by noting thicker shells from higher calcium, a misconception of environmental influence on phenotype without genetic change, confusing plasticity with evolution. A key strategy is to seek evidence of allele frequency shifts across generations to confirm evolutionary dynamics.
A population of frogs breeds in ponds near a highway. Researchers measure allele frequencies at a locus with alleles N (noise-tolerant call) and n. Over 12 years, the frequency of allele N increases from 0.15 to 0.44, with similar numbers of breeding adults each year and no translocations. Which observation best demonstrates evolution in this frog population?
Male frogs called louder on nights with heavy traffic and quieter on nights with less traffic.
Frogs moved closer to vegetation during the day to reduce desiccation in warmer months.
Traffic volume increased over the first few years and then remained relatively constant.
Individual tadpoles grew faster in ponds with higher algae levels after spring rains.
Allele N increased in frequency from 0.15 to 0.44 across many breeding seasons.
Explanation
Continuing evolution encompasses genetic adaptations to ongoing environmental challenges, like noise in this frog population. Choice B is correct because allele N for noise-tolerant calls increased from 0.15 to 0.44 over 12 years, suggesting frogs with this allele communicated better amid traffic, leading to more successful breeding. Stable breeding adult numbers and no translocations indicate selection drove this genetic shift. The long-term trend shows heritable changes propagating in the population. Choice A is a tempting distractor, describing variable call volumes based on traffic, but this misconceptions equates behavioral flexibility with evolutionary genetic change. To detect evolution, always check for allele frequency alterations across multiple generations, not situational adjustments.