7.3 Artificial Selection

1. AEach animal gradually develops the traits breeders prefer during its life, so the whole breed changes.
   A student who thinks individuals change their traits in response to selection picks this. Individuals do not acquire heritable traits by selection; the breed changes because some individuals leave more offspring.
2. BBreeders let only individuals with preferred heritable traits reproduce, so those traits become more common. Correct
   In artificial selection, humans choose which individuals reproduce. Because the chosen traits are heritable, offspring tend to carry them, and over generations the traits become more common.
3. CTraits that breeders train into the parent animals are passed on to the offspring of those animals.
   A student who thinks acquired traits are inherited picks this. Training changes an animal's body or behavior but not the alleles in its gametes.
4. DBreeders' choices cause new alleles for the preferred traits to appear in the animals as needed.
   A student who thinks variation arises because it is needed picks this. New alleles arise by random mutation; breeders can only select among the variation that exists.

CED 7.3.A.1 · Read this in Fix

1. AMean fruit mass increased, and the range of fruit masses became wider.
   A student who thinks selection creates new variation picks this. Fruit masses spanned 70 g (40–110 g) in generation 0 but only 50 g (80–130 g) in generation 15.
2. BEvery generation-15 plant had heavier fruit than every generation-0 plant.
   A student who thinks selection changes every individual in the same way picks this. The two distributions overlap from 80 to 110 g, so many generation-15 plants had lighter fruit than some generation-0 plants.
3. CMean fruit mass increased because each plant grew heavier fruit over its life.
   A student who thinks individuals change in response to selection picks this. The graphs show different plants in each generation; the population changed because heavier-fruited plants left the offspring.
4. DMean fruit mass increased, and the range of fruit masses became narrower. Correct
   The distribution shifted to heavier fruit (mean about 74 g in generation 0, about 103 g in generation 15), and the masses spanned 50 g in generation 15 compared with 70 g in generation 0.

Working Generation 0: classes 40–110 g (span 70 g); mean = (45×4 + 55×12 + 65×24 + 75×28 + 85×20 + 95×9 + 105×3)/100 = 73.7 g. Generation 15: classes 80–130 g (span 50 g); mean = (85×10 + 95×30 + 105×38 + 115×18 + 125×4)/100 = 102.6 g. The mean rose, the range became narrower, and the two distributions overlap between 80 and 110 g.

CED 7.3.A.1 · Read this in Fix

1. ANearly all plants will respond to the fungus alike, as they carry nearly the same alleles. Correct
   Propagating a few selected plants has removed most genetic variation, so the plants share nearly the same alleles. Whatever their response to the new fungus, nearly all plants will respond the same way; if they are susceptible, the whole crop is at risk.
2. BMost plants will develop resistance during their lives through exposure to the fungus.
   A student who thinks individuals acquire the traits they need picks this. A plant cannot gain heritable resistance by being exposed; resistance depends on alleles it already carries.
3. CExposure to the fungus will cause resistance alleles to arise in the plants that need them.
   A student who thinks new alleles arise because they are needed picks this. Mutations are random with respect to need, and a rare new mutation would not protect the crop now.
4. DThe crop will resist the disease, as selection has made it stronger than wild plants are.
   A student who thinks selective breeding improves organisms in general picks this. The crop was selected for traits the farmers chose, not for resistance to a fungus it has never met.

CED 7.3.A.1 · Read this in Fix

1. AReject the null hypothesis; this proves that breeding red fish caused all of the change.
   A student who thinks rejecting the null hypothesis proves a cause picks this. χ² = 72.0 > 3.84, so the result is unlikely to be due to chance, but a test cannot prove a cause, and there was no unselected control population.
2. BFail to reject the null hypothesis; a χ² value this large shows the data fit the null closely.
   A student who reverses the decision rule picks this. χ² = 72.0 is far above the critical value of 3.84, so the observed counts differ from the expected counts by more than chance would explain.
3. CReject the null hypothesis; the shift toward red is unlikely to be due to chance alone. Correct
   Expected counts are 100 red and 100 gold. χ² = 36.0 + 36.0 = 72.0, with 1 degree of freedom; the critical value at p = 0.05 is 3.84. Because 72.0 > 3.84, the null hypothesis is rejected.
4. DFail to reject the null hypothesis; gold fish still appear, so the selection had no effect.
   A student who thinks selection works only if the unselected trait disappears picks this. Gold fish fell from half of the population to 40 of 200 offspring, and χ² = 72.0 > 3.84.

Working Total = 200; expected 100 red and 100 gold. χ² = (160 − 100)²/100 + (40 − 100)²/100 = 36.0 + 36.0 = 72.0; df = 1; critical value 3.84; 72.0 > 3.84, reject the null hypothesis.

CED 7.3.A.1 · Read this in Fix

1. AA second line in which the longest 10% of beetles are bred in each generation, as in line 1
   A student who thinks repeating the treatment provides a control picks this. A replicate selected line shows whether the result is reproducible but not how body length changes without selection.
2. BA line in which the longest 10% are bred each generation and are also given extra food
   A student who thinks a control changes some other condition picks this. Extra food adds a second variable, so any difference could be due to food.
3. CA container of beetle food kept in the same conditions as line 1, with no beetles in it
   A student who thinks a control is a setup with nothing in it picks this. Without beetles, it cannot show how body length changes when parents are not selected.
4. DA line in which a random 10% of beetles are bred each generation, in the same conditions Correct
   This line differs from line 1 only in how the parents are chosen, not in how many breed. It shows how much mean body length changes without selection, for example because of changes in the rearing conditions, so any extra change in line 1 can be attributed to selection.

CED 7.3.A.1 · Read this in Fix

1. ASelection changed only how the crops look; they carry the same alleles as the wild plants.
   A student who thinks artificial selection changes only appearance picks this. The crops differ in heritable traits because farmers chose which plants reproduced in each population, which changed the alleles passed on.
2. BSelecting different traits in separate populations of one species produced very different varieties. Correct
   By artificial selection, humans change the variation found in other species. By selecting for different plant parts in different populations, farmers increased the differences between populations of one species, producing the varieties shown.
3. CFarmers' needs caused new alleles for each crop's special trait to arise in the wild plants.
   A student who thinks variation arises because it is needed picks this. Mutations arise at random; farmers selected among variants that arose without regard to their needs.
4. DEach wild plant changed its parts during its life to suit the way that farmers grew it.
   A student who thinks individuals change in response to selection picks this. The crops differ because, over many generations, farmers bred the plants that already had larger leaves, buds, stems or flowers.

CED 7.3.A.1 · Read this in Fix

1. ALess genetic variation, because only dogs with a narrow set of traits pass on their alleles Correct
   When only dogs that closely match the standard, often close relatives, are allowed to breed, many alleles present in the wider dog population are not passed on, so genetic variation within the breed falls.
2. BMore genetic variation, because breeders keep selecting for new traits in each generation
   A student who thinks selection creates variation picks this. Breeding only dogs that match a narrow standard, often relatives, reduces the variety of alleles in the breed.
3. CThe same genetic variation, because breeding changes how dogs look but not their genes
   A student who thinks artificial selection changes only appearance picks this. Choosing which dogs breed changes which alleles are passed on, so it changes the breed's genetic makeup.
4. DFewer inherited disorders, because breeders mate the healthiest and best dogs with each other
   A student who thinks selective breeding improves organisms in general picks this. Breeders select for the breed standard, and mating close relatives makes it more likely that offspring inherit two copies of a harmful recessive allele.

CED 7.3.A.1 · Read this in Fix