xxvififfPrefaceLeveling Up
questions, based on
questions the authors
use in their classrooms,
prompt students to
relate biology concepts
to their own lives. The
questions focus on one
of the following themes:
“Doing science,” “Is it
science?,” “Life choices,”
“Looking at data,” “What
do you think?,” and
“Write Now biology.”
Extensive end-of-chapter
review ensures that students
see the forest for the trees.
Pigs to the Rescue ■ 169REVIEWING THE SCIENCE
● Genes are composed of which consists of two parallel DNA,
strands of repeating units called nucleotides twisted
● into a double helix.
The four nucleotides of DNA contain the bases
adenine (A), cytosine (C), guanine (G), and thymine
(T). The nucleotides exhibit complementary base-pairing
according to rules: A can pair only with T, base-pairing
and C can pair only with G.
● DNA is wrapped around histone proteins, forming
nucleosomesnucleosome structures can. The
further compact the DNA by coiling around themselves
to form a Chromatin fichromatin fi bers further coil ber.
around themselves to form chromosomes.
● The system is composed of two CRISPR-Cas9 editing
pieces of form base pairs at precise RNA designed to
locations in a gene. This DNA-RNA interaction
guides the Cas9 proteins to the sites where they
effiresulting in a gene deletion ciently cut the DNA,
after normal repair processes take place. Additional
genetic manipulations are required to generate a gene
insertion.● (^) DNA replicationall living organisms prior to occurs in
mitosis. The double helix unwinds, and the two strands
break apart. Each strand of DNA serves as a template
from which a new strand is copied. DNA polymerase
builds each new strand of DNA using primers located
● near the origins of replication.
The reactionpolymerase chain , or PCR, is a
laboratory technique to amplify the DNA from a small
initial amount to millions of copies. Amplifi ed DNA can
then be sequenced to examine specifi c genes or mutations.
● (^) DNA is subject to damage by physical, chemical, and
biological agents, and errors in DNA replication are
common. DNA polymerase “proofreads” the DNA during
replication and corrects most mistakes. Repair proteins are
a backup repair mechanism and correct any errors that
● DNA polymerase misses.
A change to the sequence of bases in an organism’s DNA is
called a of mismatch mutations can mutation. Three types
alter a gene’s DNA sequence: substitutions, insertions,
and base is altered, it is a deletions. If only a single point
mutation.
THE QUESTIONS
The Basics
(^1) DNA replication results in
(a) two DNA molecules—one with two old strands, and one with two new strands.
(b) two DNA molecules, each of which has two new strands.
(c) two DNA molecules, each of which has one old strand and one new strand.
(d) none of the above
(^2) The DNA of cells is damaged
(a)(b) thousands of times per day. by collisions with other molecules, chemical accidents, and
(c) not very often and only by radiation.radiation.
(d) both a and b
(^3) The DNA of different species differs in the
(a)(b) sequence of bases. complementary base-pairing.
(c)(d) number of nucleotide strands. location of the sugar-phosphate portion of the DNA molecule.
(^4) Mutation
(a)(b) can produce new alleles. can be harmful, benefi cial, or neutral.
(c)(d) is a change in an organism’s DNA sequence. all of the above
(^5) Link each term with the correct defi nition.
NUCLEOTIDE 1. Two complementary bases joined by hydrogen bonds.
BASE PAIR 2. The nitrogen-containing component of a nucleotide; there are four variants of
DNA MOLECULE3. this component.A strand of nucleotides linked together
by covalent bonds between a sugar and a phosphate; two strands are
linked by hydrogen bonds between complementary bases.
BASE 4. A phosphate, a sugar, and a nitrogen-containing base.
(^6) In the diagram of replication shown here, fi ll in the blanks with the
appropriate terms: (a) base pair, (b) base, (c) nucleotide, (d) template strand, (e) newly synthesized strand, (f) separating strands.
154-171_BioNow2e_Ch09_N.indd 169 10/18/17 5:06 PM
Dog Days of Science ■ 133
Try Something New
to the same species as the red fox:^10 The silver fox (see “The New Family Pet?” on page 127) belongs Vulpes vulpes. Two silver foxes
always breed true for silver offspring. A silver fox bred to a red fox will produce either all red offspring or, occasionally, half red
and half silver offspring. Red foxes bred together usually produce all red offspring, but they occasionally produce silver offspring in
the ratio of 3 red to 1 silver. (these predicted results.) Which of the following statements is/are Hint: Draw Punnett squares showing
consistent with the information provided here about inheritance of coat color in Vulpes vulpes? (Select all that apply.)
(a)(b) Red foxes are all homozygous. Silver foxes are all homozygous.
(c)(d) Red is dominant to silver. Some silver foxes are homozygous and some are heterozygous.
(e) Some red foxes are homozygous and some are heterozygous.
tomatoes. You love the taste of Big Boys, but you think it’s easier^11 In your garden you grow Big Boy (round) and Roma (oval)
to slice Roma tomatoes. You decide to cross-pollinate a Big Boy and a Roma to see whether you can create a new strain of “Long
Boys.” In the fiwould you explain this result? What would your next cross be? rst generation, all of the tomatoes are round. How
Write out the cross in a Punnett square, using parental genotypes. What proportion of the next generation, if any, would be oval?
(^12) For several hundred years, goldfi sh have been selectively bred
in China and Japan for body color and shape, tail shape, bulging eyes, and even fl eshy head growths.
Wild goldfishPet-shop goldfishBlack moorgoldfish
Imagine that you have a tank of pet-shop goldfiadded a couple of black moor goldfi sh, hoping that they will breed. sh and have just
When the eggs laid by the black moor female (P generation) hatch and the young fi sh (F
to see that they are orange. How would you explain this result in^1 generation) begin to develop, you are shocked
terms of the inheritance of body color in goldfiexperiment could you conduct to test your hypothesis? sh? What breeding
and Gordon Lark published the results of its research on coat^13 In 2009, a large team of researchers including Elaine Ostrander
inheritance in dogs. The study began by focusing on dachshunds and Portuguese water dogs, but then widened to more than 80
breeds. The scientists were able to explain 95 percent of the variation in dog coat types with just two alleles at each of three
genes, each inherited independently of the other. These genes coded for hair length (L/l), wave or curl in the coat (W/w), and
the presence of “furnishings” (and eyebrows often seen in wire-haired dogs (see photo). Long-F/f), which are the moustache
haired dogs carry two copies of the long-hair allele, which is
recessive to the short-hair allele. Dogs with furnishings can be either homozygous or heterozygous for the furnishings allele; dogs
without furnishings are homozygous for the no-furnishings allele.
a. At the hair length and furnishings genes, what is the genotype of a long-haired dog without furnishings?
b. At the hair length and furnishings genes, what are all the possible genotypes of a short-haired dog with furnishings?
c. Create a Punnett square of two dogs heterozygous for hair length and furnishings. What is the offspring phenotype ratio for
those two traits?
Leveling Up
(^14) Doing science Do you want to get involved in dog research?
If you have a purebred as a pet, you can. Find out whether the Dog Genome Project at the National Institutes of Health is doing
research on your pet’s breed. If they are, you can send in a swab of your dog’s saliva and contribute to science. Visit the NIH website
(http://research.nhgri.nih.gov/dog_genome) for more information.
(^15) News Is it science? printed a story about a woman who, after repeatedly watching The November 18, 2003, issue of Weekly World
the movie who looked like the main character, an ogre named Shrek. Like Shrek while taking fertility drugs, gave birth to a baby
Shrek, the newborn had dull green skin, a large flprotruding from stems. From what you know about genetics, do you at nose, and ears
think it’s possible for a developing fetus to change so drastically (from a normal-looking baby to a “Shrek” baby) because its mother
was obsessed with a movie? Why or why not? How would you explain your answer to someone who believed this news report?
(^16) What do you think? Many people are critical of those who
breed or purchase purebred dogs, arguing that there are many mixed-breed dogs waiting to be adopted from shelters. They also
point out that mixed-breed dogs are less likely than purebred dogs to suffer from genetic diseases. Those who prefer a particular
breed argue that there is a strong genetic inflpersonality and behavior, and that they don’t want any surprises uence on dog
when they add a new member to their family. What do you think?
For more, visit digital.wwnorton.com/bionow2 for access to:
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228 ■ CHAPTER 12 Mechanisms of Evolution
individual’s ability to survive and may result in offspring that are^2 Unlike natural selection, is not related to an
less well adapted to survive in a particular environment.(a) genetic drift
(b)(c) sexual selection directional selection
(d) convergent evolution
is true?^3 Which of the following statements about convergent evolution
(a) It demonstrates how similar environments can lead to different physical structures.
(b) It demonstrates how similar environments can lead to the same physical structures.
(c) It demonstrates that similarity of structures is due to descent from a common ancestor.
(d) It demonstrates that similarity of structures is due to random chance.
frequencies in^4 Evolution is most accurately described as a change in allele over time.
(a)(b) an individuala species
(c)(d) a populationa community
Challenge Yourself
reproduce?^5 In a population, which individuals are most likely to survive and
(a) The individuals that are the most different from the others in the population.
(b)(c) The individuals that are best adapted to the environment.The largest individuals in the group.
(d) The individuals that can catch the most prey.
large individuals consistently survive and reproduce at a higher^6 A study of a population of the goldenrod wildfl ower fi nds that
rate than small or medium-sized individuals. Assuming size is an inherited trait, the most likely evolutionary mechanism at work
here is(a) disruptive selection.
(b)(c) directional selection.stabilizing selection.
(d) natural selection, but it is not possible to tell whether it is disruptive, directional, or stabilizing.
be very successful at surviving (natural selection), but not pass on^7 Explain how, because of sexual selection, an individual might
genes to the next generation.
THE QUESTIONS
The Basics
individuals in one small group of a large population (^1 The founder effect is a type of (genetic drift / gene flestablish a new ow) in which
distant population / are the only survivors) and then reproduce.
● Natural selection for inherited traits occurs in three
common patterns: directional, stabilizing, and disruptive.
● In individuals at one phenotypic directional selection,
extreme of a given genetic trait have an advantage over
all others in the population.
● In individuals with intermediate stabilizing selection,
phenotypes have an advantage over all others in
● the population.
During individuals with either disruptive selection,
extreme phenotype have an advantage over those with an
intermediate phenotype.
● In distantly related organisms convergent evolution,
(those without a recent common ancestor) evolve
similar structures in response to similar environmental
challenges.
● All mechanisms of evolution depend on the genetic
variation provided by new alleles created by mutation.
● Sexual selection when a trait increases occurs
an individual’s chance of mating even if it decreases
that individual’s chance of survival.
● (^) Gene flof alleles between separate ow is the exchange
populations.
● Genetic drift allele frequencies produced is a change in
by survival and reproduction in random differences in
a small population, and most dramatically occurs through
one of two processes: a genetic bottleneck or the
founder effect.
● A when a drop in the size of a genetic bottleneck occurs
population leads to a loss of genetic variation in the new,
rebounded population.
● The when a few individuals from a founder effect occurs
large population establish a new population, leading to a
loss of genetic variation in the new, isolated population.
REVIEWING THE SCIENCE
210-229_BioNow2e_Ch12.indd 228 10/18/17 5:41 PM
Battling Resistance ■ 229
(b) Small mice cannot reach the seed shelf, and large mice are easily seen by hawks circling above. Medium-sized mice
therefore survive and reproduce better than both small and large mice.
(c) Small mice can easily cross the yard to the vegetable garden, and large mice can easily reach the seed shelf. Medium-sized
mice have trouble with the seed shelf and are seen by hawks in the yard. Small and large mice survive and reproduce much
(d) better than medium-sized mice.All of these are examples of stabilizing selection.
(e) None of these are examples of stabilizing selection.
Leveling Up
(^12) What do you think? One way to prevent a small population
of a plant or animal species from going extinct is to deliberately introduce some individuals from a large population of the same
species into the smaller population. In terms of the evolutionary mechanisms discussed in this chapter, what are the potential
benefipopulation to another? Do you think biologists and concerned ts and drawbacks of transferring individuals from one
citizens should take such actions?
explores the mechanisms of evolution through fi^13 Write Now biology: mechanisms of evolution ve selected short This assignment
stories from Answer the questions associated with each story.Welcome to the Monkey House by Kurt Vonnegut Jr.
“Harrison Bergeron”What message is this story trying to send? Cite examples from
the story and relate them to the mechanisms of evolution from this chapter.
“Welcome to the Monkey House”Is this story an example of sexual selection? Why or why not?
Cite examples from the story and from this chapter to support your thinking.
“The Euphio Question”If technology could produce such an instrument, how would it
affect the evolution of humans? What about the evolution of other species on Earth?
“Unready to Wear”Relate this story to as many of the mechanisms of evolution
from this chapter as you can. Cite examples from the story and the chapter to support your thinking.
“Tomorrow and Tomorrow and Tomorrow”Do you think these types of drugs are a good or bad thing?
Where would you draw the line on technology’s ability to extend life? How would drugs like these affect the natural selection and
evolution of humans? What about the evolution of other species on Earth?
Try Something New
neighboring locations that have very different environments are^8 Two large populations of the same species found in
observed to become genetically more similar over time. Which of the four main evolutionary mechanisms is the most likely cause of
this trend? Justify your answer.
Tasmania (and formerly mainland Australia as well), experienced^9 The Tasmanian devil, a marsupial indigenous to the island of
a population bottleneck in the late 1800s when farmers did their best to eradicate it. After it became a protected species, the
population rebounded, but it is now experiencing a health crisis putting it at risk for disappearing again. Many current Tasmanian
devil populations are plagued by a type of cancer called devil facial tumor disease, which occurs inside individual animals’ mouths.
Afflone animal to another during mating rituals that include vicious icted Tasmanian devils can actually pass their cancer cells from
biting around the mouth.Unlike the immune systems of other species, including humans,
the Tasmanian devil’s immune system does not reject the passed cells as foreign or nonself (as we reject a liver transplant from an
unmatched donor), but accepts them as if they were their own cells. Why would a population bottleneck result in the inability of
one devil’s immune system to recognize another devil’s cells as foreign?
(^10) Global warming is causing more and more ice to melt each
year at far-northern latitudes, exposing more bare ground than ever before. These vast areas of brown ground coloration make
polar bears (which are white) much more conspicuous to their prey. Recently, an infant polar bear was born with brown fur.
This polar bear survived to adulthood and has sired several offspring with brown fur. Which of the following is a plausible
explanation of how the brown fur trait appeared in these polar bears?
(a) A polar bear realized it would be better to be brown in order to hide more effectively. It induced mutations to occur in its fur
pigment gene, which resulted in a change in pigment from white to brown fur.
(b) One or more random mutations occurred in the fur pigment gene in an individual polar bear embryo, which resulted in a
(c) change in pigment from white to brown fur.Increased temperatures due to global warming caused targeted
mutations in the fur pigment gene in an individual polar bear embryo, which resulted in a change in pigment from white to
(d) brown fur.A female polar bear realized it would be better for her offspring
to be brown and therefore mated with a grizzly bear to achieve this result.
(^11) stabilizing selection has occurred over the past 10 years in the In the garden shed belonging to one of this text’s authors,
house mouse, example of stabilizing selection?Mus musculus. Which of the following scenarios is an
(a) Small and medium-sized mice cannot reach the seed shelf in the shed and therefore are at a disadvantage for fi nding food,
so they do not survive and reproduce as well as large mice do.
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210-229_BioNow2e_Ch12.indd 229 10/18/17 5:41 PM
End-of-chapter
questions follow
Bloom’s taxonomy,
moving from review (The
Basics), to synthesis
(Try Something New),
to critical thinking
(Challenge Yourself), to
application (Leveling Up).
Reviewing the Science
identifies each chapter’s
key science concepts,
providing students with a
guide for studying.