End-of-topic test: Artificial Selection

Unit 7 · Topic 7.3 end-of-topic test

Suggested time: about 47 minutes. Answer everything, then press Submit the test to see the feedback and scoring guides.

Answer every question. For each multiple-choice question, pick one option and press Check; the feedback gives the reasoning. For the free-response questions, write one short sentence for each step of your reasoning, each on its own line, and make every link clear (so, because, therefore). That is what the exam’s ‘paragraph form’ means for you: linked sentences, not bullet points. Then open the scoring guide and mark your own work against it.

Question 1

Which of the following is an example of artificial selection?

A. A gardener saves seed only from the plants whose flowers open earliest B. In a farmer’s field, a drought kills the shallow-rooted plants, and the deep-rooted plants set seed C. Bees visit the plants with the largest flowers most often, so those plants set the most seed D. In a nursery, a fungus kills the thin-stemmed seedlings, and the thick-stemmed seedlings set seed

Question 2

A breeder keeps a line of goats and, each generation, breeds only from the goats with the longest coats.

Which of the following does the breeder change?

A. The alleles carried by the chosen goats B. The length of coat the chosen goats themselves grow C. The rate at which new alleles arise D. Which goats breed

Question 3

Artificial selection and natural selection are alike in which of the following ways?

A. The environment alone decides which individuals get to breed B. People alone decide which individuals get to breed C. The breeding individuals’ alleles pass to the offspring by ordinary inheritance D. Individuals develop the wanted trait in their lifetime and pass it on

Question 4

A beet line: the parents used in each breeding cycle and the mean root mass of their offspring.

Researchers breed a beet line. In each cycle they grow 200 plants in one greenhouse, weigh every root, and cross the 20 plants with the heaviest roots to make the next cycle’s seed. The table shows the mean root mass of each cycle’s offspring.

Which of the following explains why the mean root mass rose from cycle to cycle?

A. Only heavy-rooted plants bred, so their alleles made up a larger share each cycle B. Each cycle’s plants grew heavier roots in the greenhouse and passed that growth on C. Hand-crossing itself made the roots heavier D. Which plants bred varied by chance from cycle to cycle

Question 5

A guinea-pig line bred from pups that reach 700 g by eight weeks: the percent of such pups in generations 0 to 4.

A breeder of guinea pigs keeps, each generation, only the pups that reach 700 g by eight weeks to breed from. The table shows the percent of pups reaching 700 g by eight weeks in each generation.

Which of the following is the best prediction of the percent of pups reaching 700 g by eight weeks in generation 5?

A. 85% B. 88% C. 91% D. 96%

Question 6

A flock bred from dark-egg hens only: the percent of hens laying dark-brown eggs in years 0 to 4.

A farmer breeds hens and, each year, hatches chicks only from the hens that lay dark-brown eggs. The table shows the percent of hens laying dark-brown eggs each year.

Which of the following explains why each year’s rise is smaller than the one before?

A. The farmer hatches chicks from fewer and fewer hens each year B. Hens laying dark-brown eggs lay fewer eggs each year than pale-egg hens C. Alleles for dark-brown eggs grow weaker as more and more hens carry them D. Fewer hens carry pale-egg alleles each year, so choosing removes fewer of those alleles

Question 7

A breeder saves seed only from purple-flowered pea plants. Purple flower color is dominant to white. After eight generations, a few white-flowered plants still appear each year.

Which of the following explains why white-flowered plants keep appearing?

A. The breeder saved seed from white-flowered plants by mistake B. New white alleles arise by mutation in many plants each year C. Some purple-flowered plants carry a white allele and pass it on D. Purple alleles change into white alleles in the seed

Question 8

Two bean lines from one seed mixture: how the parents were chosen, the mean number of different alleles per gene at generations 0 and 10, and the mean pod length at generation 10.

A seed cooperative founds two bean lines from one seed mixture and grows 300 plants of each line every generation. In the long-pod line, the 60 plants with the longest pods supply the next generation’s seed; in the random line, 60 plants chosen at random supply it. After ten generations the cooperative counts the different alleles at 20 genes. The table shows the results.

Which of the following explains why the long-pod line carries fewer alleles per gene than the random line?

A. Every generation the shorter-podded plants were left out, so alleles only they carried were lost B. Choosing long pods caused mutations that destroyed alleles in the long-pod line C. Long-podded plants carry fewer alleles per gene than short-podded plants do D. The random line gained new alleles by mutation in every generation

Question 9

A breeder wants a line of quail with heavier eggs, but she also wants the line to keep as much of the flock’s genetic variation as it can. Each generation she breeds from one group of her 100 hens.

Which of the following groups of breeders loses the fewest alleles from the line?

A. The 5 hens with the heaviest eggs B. The 20 hens with the heaviest eggs C. The 50 hens with the heaviest eggs D. The 5 hens with the heaviest eggs and 5 hens picked at random

Question 10

Two rabbit lines from one group: mean ear length against generation. The selected line is solid with filled points; the control line is dashed with open points.

A rabbit breeder keeps two lines from one group of rabbits. In the selected line, only the rabbits with the longest ears breed each generation; in the control line, rabbits picked at random breed. The graph shows each line’s mean ear length in centimeters against generation.

Which of the following statements is supported by the graph?

A. The mean ear length rose each generation in the selected line B. The mean ear length rose each generation in the control line C. The mean ear length in the selected line fell after generation 2 D. In generation 4, the control line’s mean ear length was 12.0 cm

Question 11

A pepper line bred from plants with 8–10 cm fruit: the shortest and longest fruit and the percent of fruits 8–10 cm long, in generations 0, 3 and 6.

Growers breed a pepper line in one greenhouse, with the same light, soil and watering every generation. Each generation they save seed only from plants whose fruits are 8 cm to 10 cm long. The table shows the results.

Which of the following explains why the range of fruit lengths narrowed from generation 0 to generation 6?

A. The same watering every generation made every fruit grow to a similar length B. Plants with the shortest and the longest fruit left no seed, so the alleles they alone carried were lost C. Choosing 8–10 cm fruit caused mutations toward that length D. Fruits grew or shrank in the greenhouse toward 8–10 cm, and the plants passed the change on

Question 12

A student measures the lengths of 30 feathers to the nearest millimeter. The shortest feather is 21 mm and the longest is 58 mm. She wants four bins of equal width that cover every feather.

Which of the following is the smallest whole-millimeter bin width that does this?

A. 9 mm B. 10 mm C. 15 mm D. 19 mm

Question 13

Body lengths of one sample of beetles, to the nearest millimeter, in five 2 mm bins.

A student measures the body lengths of the beetles in one sample, to the nearest millimeter, and draws the histogram below.

Which of the following statements is supported by the histogram?

A. Every beetle in the sample is at least 8 mm long B. More beetles are 12 mm or longer than are 9 mm or shorter C. The beetles are spread evenly across the lengths from 6 mm to 15 mm D. Most of the beetles are between 8 mm and 13 mm long

Question 14

Shell widths of one pond sample of snails, to the nearest millimeter, in five 4 mm bins.

A student measures the shell widths of the snails in one pond sample, to the nearest millimeter, and draws the histogram below.

How many of the snails have a shell width of 24 mm or more?

A. 13 B. 19 C. 22 D. 38

Question 15

Twelve radish masses in grams, in order, smallest first.

A student measures the masses of twelve radishes to the nearest gram and puts them in order, smallest first, as the table shows.

Which of the following is the lower quartile of the masses?

A. 20 g B. 22 g C. 24 g D. 28 g

Question 16

Leaf lengths of 60 seedlings; a gridline every 4 mm.

A student draws the box plot below of the leaf lengths of 60 seedlings.

Which of the following statements is supported by the box plot?

A. Half of the 60 leaves are longer than 48 mm B. Half of the 60 leaves are between 40 mm and 48 mm long C. Most of the 60 leaves are between 48 mm and 68 mm long D. The 60 leaves are spread evenly from 28 mm to 68 mm

Question 17

Daily milk yield of 40 cows before the breeding began (upper plot) and of 40 cows six generations later (lower plot).

A dairy farmer breeds, for six generations, only from the cows with the highest milk yield. The box plots show the daily milk yield of 40 cows before the breeding began and of 40 cows six generations later.

Which of the following describes the change from before to after?

A. The center moved up and the spread narrowed B. The center moved up and the spread widened C. The center moved down and the spread narrowed D. The center moved down and the spread widened

Question 18

A breeder measures the hind-leg length of every cricket in a line. Over ten generations the mean stayed at 24.0 mm while the standard deviation fell from 3.2 mm to 1.1 mm.

Which of the following would box plots of generation 0 and generation 10 show?

A. The center moved down and the spread narrowed B. The center stayed the same and the spread widened C. The center stayed the same and the spread narrowed D. The center moved up and the spread stayed the same

How to tackle the free-response questions. Read the verb first: describe asks what you see or know; explain asks why or how, so name the mechanism; predict asks what will happen and why; justify asks for the evidence that supports a claim. Each point is earned by one idea, stated in a sentence that names the thing and the mechanism. Extra words earn nothing; a wrong extra can lose the point. If there is a figure or table, use what it shows. When you finish, check the box for each point your answer earns and compare your sentences with the full-credit answer.

Free response 1 · Analyze Data · 4 points

A shepherd keeps a flock of 40 breeding sheep and, each generation, breeds only from the ten sheep with the heaviest fleeces. The histograms show the fleece mass, in kilograms, of the 40 sheep in generation 0 and of the 40 sheep in generation 5.

Fleece mass of the 40 sheep of generation 0 (left) and of generation 5 (right), in six 0.5 kg bins; each bar carries its count.

(a) Identify the most common fleece-mass range in generation 5. (1 point)

A full-credit answer: The most common range in generation 5 is 4.0–4.4 kg: the tallest bar, 18 of the 40 sheep.

Check the box for each point your answer earns

4.0–4.4 kg (the tallest bar of the generation-5 histogram). Accept with or without the count, 18 sheep.

Common slip: Reading the tallest bar of generation 0, 3.0–3.4 kg. The question asks about generation 5.

(b) Describe how the spread of fleece mass changed from generation 0 to generation 5. (1 point)

A full-credit answer: The spread narrowed.
In generation 0 the sheep filled all six bins, 2.0 kg to 4.9 kg.
In generation 5 they filled four bins, 3.0 kg to 4.9 kg, and 30 of the 40 sat in two bins.

Check the box for each point your answer earns

the spread narrowed, with evidence from the histograms (six bins filled became four; the range 2.0–4.9 kg became 3.0–4.9 kg; or 30 of the 40 sheep sit in two bins). Do not award: a change with no direction named.

Common slip: Writing that the spread ‘changed’. Say which way: it narrowed, and give the bins or the range that show it.

(c) Support the claim that the shepherd’s choice of parents raised the flock’s fleece mass, using data from the histograms. (1 point)

A full-credit answer: The tallest bar moved from 3.0–3.4 kg in generation 0 to 4.0–4.4 kg in generation 5, and sheep with fleeces of 4.0 kg or more rose from 5 of 40 to 24 of 40.
Only the ten heaviest-fleeced sheep bred each generation, so their alleles for heavy fleece passed to the lambs and made up a larger share each generation.
So the shepherd’s choice raised the flock’s fleece mass.

Check the box for each point your answer earns

evidence from the histograms that fleece mass rose (the tallest bar moved from 3.0–3.4 kg to 4.0–4.4 kg; or sheep of 4.0 kg or more rose from 5 to 24 of 40; or the two lightest bins emptied) AND the reasoning that only the heaviest-fleeced sheep bred, so their alleles made up a larger share of the flock each generation.

Common slip: Quoting the histograms without saying why the chosen sheep’s lambs carried heavier fleeces. The claim needs the evidence and the reason that links the evidence to the shepherd’s choice.

(d) Explain how breeding only from the ten heaviest-fleeced sheep each generation affected the flock’s genetic variation for fleece mass. (1 point)

A full-credit answer: Each generation, only ten of the 40 sheep bred.
Only those ten sheep’s alleles passed to the lambs.
Alleles carried only by the other 30 sheep were not passed on and were lost.
Five generations of losses left the flock with fewer alleles for fleece mass, so its genetic variation fell.

Check the box for each point your answer earns

the variation fell, because only the ten chosen sheep bred each generation, so alleles carried only by the unchosen sheep were not passed on and were lost, leaving the flock fewer alleles.

Common slip: Writing that the flock lost variation ‘because the fleeces became similar’. The similar fleeces are the result; the cause is the alleles that left with the unchosen sheep.

Free-response score: 0 of 4

Free response 2 · Analyze Data · 4 points

A barley breeder keeps two lines in one field. In the selected line, only the plants with the most grains per ear supply the next generation’s seed. In the control line, plants picked at random supply it. The graph shows each line’s mean grains per ear against generation.

Mean grains per ear against generation for the selected line (solid, filled points) and the control line (dashed, open points); a gridline every 2 grains per ear.

(a) Identify the selected line’s mean grains per ear in generation 3. (1 point)

A full-credit answer: In generation 3 the selected line’s mean was 54 grains per ear.

Check the box for each point your answer earns

54 grains per ear (read from the solid line at generation 3).

Common slip: Reading generation 3 on the control line, 40 grains per ear. The selected line is the solid line with filled points.

(b) Describe the pattern in the selected line’s mean grains per ear from generation 0 to generation 6. (1 point)

A full-credit answer: The selected line’s mean grains per ear rose, from 40 to 58 grains per ear.
The rises were 6, 4, 4, 2, 2 and then 0 grains per ear, so the rise slowed and stopped between generations 5 and 6.

Check the box for each point your answer earns

the mean grains per ear rose (from 40 to 58 grains per ear). Accept with or without: the rise slowed and levelled off by generation 6.

Common slip: Writing that the mean ‘changed’ or ‘was different’. Name the direction: it rose.

(c) Support the claim that the breeder’s choice of parents, rather than the field’s growing conditions, caused the change in the selected line. (1 point)

A full-credit answer: The control line grew in the same field but bred from plants picked at random, and its mean stayed near 40 grains per ear.
The two lines differed only in who chose the parents.
So the change in the selected line came from the breeder’s choice, not from the field.

Check the box for each point your answer earns

the control line, grown in the same field, stayed near 40 grains per ear (evidence) AND the only difference between the lines was the choice of parents, so that choice caused the change (reasoning).

Common slip: Quoting the selected line alone. The claim is about the cause, so the control line, grown in the same field, is the evidence.

(d) Predict how the selected line’s mean grains per ear will change between generation 6 and generation 10 if the breeder keeps choosing the same way. Justify your prediction. (1 point)

A full-credit answer: The mean will stay near 58 grains per ear, or rise only a little.
Each generation, only the plants with the most grains bred, so their alleles now make up nearly all of the line.
Few alleles for fewer grains are left to remove, so choosing changes the mean by less and less.

Check the box for each point your answer earns

the mean stays near 58 grains per ear or rises only a little (prediction) AND few alleles for fewer grains per ear remain to be removed, so choosing changes the mean by less each generation (justification). Accept: the line has little variation left for grains per ear.

Common slip: Predicting that the mean keeps rising by about 6 grains per ear each generation. The rises shrank to nothing between generations 5 and 6.

Free-response score: 0 of 4

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Multiple choice checked: 0 of 18 correct.

Next: Counting alleles, not rabbits