CWI BIOL 112 Exam 2

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A windstorm transports a few seeds of a plant species from Island A, where the species is abundant, to Island B, where prior to this event the plant species was not found. The environmental conditions on the two islands are very similar, but the islands are located far away from one another. Over time, a small population of this plant becomes established on Island B. A biologist samples plants on both islands and finds that allele frequencies on Island A differ substantially from allele frequencies on Island B at several genetic loci not known to affect survival or reproduction. Based on this information, the observed genetic changes mostly likely resulted from

Genetic Drift

The largest unit within which gene flow can readily occur is ____

a species

What does the biological species concept use as the primary criterion for determining species boundaries, i.e., whether two populations are the same species or different species?

no gene flow

A small number of birds arrive on an island from a neighboring larger island. This small population begins to adapt to the new food plants available on the island, and the frequency of beak sizes in the population begin to change. About twice a year, one or two more birds from the neighboring island arrive. These new arrivals __

tend to retard adaptation to the new food plants

Which two of the following have operated to increase divergence between mosquitofish populations on Andros?
1. improved gene flow
2. bottleneck effect
3. sexual selection
4. founder effect
5. natural selection

3 and 5

Which type of reproductive isolation operates to keep the mosquitofish isolated, even when fish from different ponds are reunited in the same body of water?

behavioral isolation

The production of sterile mules by interbreeding between female horses (mares) and male donkeys (jacks) is an example of ____

reduced hybrid fertility

Theoretically, the production of sterile mules by interbreeding between female horses (mares) and male donkeys (jacks) should

strengthen prezygotic barriers between horses and donkeys

Of the 59 matings in the experimental groups, how many were between like-adapted flies (flies adapted to the same medium)?


Which of the following statements is best supported by the data on matings in the experimental groups?

The starch-adapted flies and maltose-adapted flies are not different species, but a reproductive barrier is forming between the populations.

Which of the following statements is supported by the data from the control group matings?

Flies were about as likely to mate with flies from different starch-adapted populations as with flies from their own starch-adapted population.

A similar control experiment was performed with flies adapted to maltose, and similar results were obtained. What were these control experiments testing?

These control experiments tested whether flies were more likely to choose mates from their own population than from another population adapted to the same medium.

When populations are separated, they may experience genetic drift. What is genetic drift?

A change in allele frequencies caused by random events

Why are the large finches now living on the Galápagos Islands different from the original source population from a nearby island?

The separation of habitats reduced gene flow between the populations. Genetic drift occurred in the two populations. Natural selection favored individuals that were more fit in the new environment.

Which of the following statements about reinforcement is true?

Reinforcement is a type of natural selection.

A subset of a population of birds disperses from its habitat on the mainland and colonizes a nearby island. The birds, after a period of time, become reproductively isolated. The island sinks and the population of birds that lived on the island returns to its original habitat on the mainland. Which of the following statements about these bird populations is true?

The populations will not be able to interbreed because they are different species.

A population of birds colonizes an area in which the insects upon which they feed live inside trees. Which of the following events accounts for an observed increase in average beak size in the bird population over time?

Increased fitness of large-beaked birds, leading to natural selection

True or false? A flood that separates a population of frogs onto opposite sides of a lake is an example of a vicariance event that may result in allopatric speciation.


Which of the following factors would not contribute to allopatric speciation?

Gene flow between the two populations is extensive

Sympatric speciation is ___

the appearance of a new species in the same area as the parent population

Gametes from two plant species combine and produce a haploid zygote, and that zygote develops into a haploid, hybrid plant. Why is the hybrid plant sterile?

Meiosis cannot occur The cells do not contain homologous chromosomes.

The sequence of events illustrated in this figure results in a fertile hybrid plant called an allopolyploid. Which of the following statements is the most complete description of an allopolyploid?

It contains more than two sets of chromosomes, which are derived from two species.

Plant species F has a diploid number of 8. Plant species G has a diploid number of 10. What would be the diploid number of an allopolyploid hybrid of species F and species G?
Enter your answer as a whole number.


What role does nondisjunction play in the formation of a fertile allopolyploid hybrid?

It doubles the chromosome number in the hybrid

Which of the following has been shown to cause speciation most rapidly?


Two researchers experimentally formed tetraploid frogs by fertilizing diploid eggs from Rana porosa brevipoda with diploid sperm from Rana nigromaculata. When they mated these tetraploid frogs with each other, most of the offspring that survived to maturity were tetraploid, with chromosome sets of both diploid parent species. Based on these results, if this type of tetraploid formed in the wild, what would be the result? (Reference: Y. Kondo and A. Kashiwagi. 2004. Experimentally induced autotetraploidy and allotetraploidy in two Japanese pond frogs. Journal of Herpetology 38(3):38192.)

The tetraploids would be reproductively isolated from both parent species.

A hybrid zone is properly defined as ___

an area where mating occurs between members of two closely related species, producing viable offspring

In Europe, there is a long narrow hybrid zone, shown in red on the map, between the high-altitude habitat of the yellow-bellied toad and the lowland habitat of the fire-bellied toad. Despite this, there is little gene flow between the two species. Select the correct explanation.

Hybrids have poor survival and reproduction and thus produce few viable offspring with members of either parent species

Hybrids are most likely to occur if species

are classified as members of the same genus

The phenomenon of fusion is likely to occur when, after a period of geographic isolation, two populations meet again and

an increasing number of viable, fertile hybrids is produced over the course of generations

In hybrid zones where reinforcement is occurring, which of the following should be REDUCED?

gene flow between distinct gene pools

Reinforcement in a hybrid zone is most likely to occur when ___

hybrids have lower fitness than either parent population

Male frogs give calls that attract female frogs to approach and mate. Researchers examined mating calls of closely related tree frogs in South America. In areas of allopatry, closely related species have similar songs. In areas of sympatry, reinforcement is expected to occur. What would you expect if you compare the calls of the two species in sympatry vs. in allopatry?

calls would be more different in areas of sympatry

Based on the examples discussed in Figures 24.12 and 24.15, the most likely explanation for the recent decline in cichlid species diversity in Lake Victoria (other than predation by introduced Nile perch), is ___


Hybrid zones provide an opportunity to investigate ___

the evolution of reproductive isolation

Before examining an example of speciation in the Galápagos, consider two species of large cats. Lions and tigers live on different continents and differ in many ways.
(Panthera leo)
continent- Africa
habitat- savannas and grasslands
social behavior- live and hunt in groups
appearance- no stripes

(Panthera tigris)
Continent- Asia
Habitat- Forests
Social behavior- Live and hunt alone

In nature, they do not hybridize, or interbreed. Therefore, according to the biological species concept, lions and tigers are separate species. However, in captivity, humans have been able to interbreed lions and tigers. Hybridization of a male lion and a female tiger forms a liger. Ligers are able to produce fertile offspring.
Based on this information, do you still think lions and tigers are separate species? (All responses will be marked correct.)


In the early 1970s, Drs. Peter and Rosemary Grant began studying Darwin’s finches and significantly extended our knowledge of the different species and their behaviors. On the island of Daphne Major, the Grants focused on three closely related species within the genus Geospiza. The table summarizes some of the distinguishing traits of each species.

G. scandens
Body size- medium
beak- pointed
diet- specialized on cactus

G. fortis
Body size- medium
beak- robust
diet- specialized on small ground seeds

G. magnirostris
body size- large
beak- large
diet- specialized on large, hard seeds

The Grants did experiments that demonstrated that each species on Daphne chooses mates of their own species over other species. On rare occasions, species will hybridize and create viable offspring, but this is extremely infrequent. The three species are still distinct enough that they are considered separate species.

In 1981, a single bird appeared on Daphne that was not any of the three species described above. The Grants called him "5110." Watch the video to learn more about 5110.

What did the Grants observe about 5110? Drag the terms on the left to the appropriate blanks on the right to complete the sentences.

Bird 5110 was larger than other birds on the island, which earned him the nickname Big Bird. The song of 5110 was different from the songs of other bird species on the island. The Grants performed genetic testing on 5110 and determined that he was homozygous for a rare allele. They also determined that he was hatched on a neighboring island.

When 5110 first appeared, the Grants did not know how to classify him. Where did he come from? Was he a new species of finch, or was he an infertile hybrid of known species? If birds prefer to mate with other birds from their own species, what would 5110’s fate be on Daphne where there were no other birds like him?
The Grants performed genetic testing on 5110 and determined that he was a hybrid, with a mixture of G. fortis and G. scandens genes. He was most likely the product of a G. fortis-scandens hybrid backcrossed (mated back) to G. fortis.

Which of the models correctly shows the Grants’ hypothesis for 5110’s parentage?

G.fortis——˅—–G. scandens Fortis-scandens hybrid——˅—-G fortis Big bird

The original Big Bird went on to breed with three females on Daphne: another hybrid and two G. fortis females. The descendants of 5110 shared his unique call and unique genotype. Although 5110 bred with other species (because he was the only Big Bird then), his offspring only bred with other Big Birds.
Watch the video to learn more about the Big Bird lineage and how it was established on Daphne.
The Big Bird and his descendants are a rare glimpse at how a natural hybridization event can form a new lineage from two species that live in the same area. However, there is not yet scientific consensus about whether the Big Bird lineage should be considered its own species. There is evidence for and against its classification as a separate species.

Using the biological species concept as your guide, sort the following observations based on whether they support the notion that the Big Bird lineage is a separate species or whether they refute the notion that it is a separate species.

Supports separate species– Big Birds have their own unique call.There is no gene flow in or out of the Big Bird population.Big Bird males hold territories in and around territories of other species but breed only with Big Bird females. Refutes separate species– Big Bird males can breed with G. fortis females.

According to the biological species concept, distinct species are defined by reproductive isolation–that is, by a lack of interbreeding and a failure to produce viable or fertile offspring if they do mate. In some cases, reproductive isolation may not be complete, and there may be rare instances of interbreeding. As long as hybridization is rare, biologists generally classify species as distinct under the biological species concept.
Given what you’ve learned about the biological species concept, should G. fortis and G. scandens continue to be considered separate species?


Which of the following statements about adaptive radiation is correct?

Adaptive radiation occurs within a single lineage

Which organisms are not examples of an adaptive radiation?

Mammals and reptiles in the post-dinosaur age

True or false? Convergent evolution is said to have occurred if the mouse species on two islands with similar habitats are found to have similar characteristics even though they originated from different species that did not have these characteristics.


Which Anolis lizard ecomorph has long legs?


Which of the following statements about the evolution of Anolis lizards in the Caribbean islands is true?

The phylogeny of ecomorphs on a given island reveals that adaptive radiation has taken place.

What was the main selective pressure behind the evolution of different Anolis lizard species in the Caribbean?

Specific ecological niches

True or false? The evolution of different ecomorphs on the Caribbean islands is an example of stabilizing selection.

false The evolution of different ecomorphs is an example of disruptive selection. Each new ecomorph had characteristics that were ideal for a particular habitat, but as these characteristics developed, the lizards lost the ability to survive effectively in the other habitats on the island.

Feathers either play a role, or may have played a role, in ____

extended hops, gliding, flight, courtship

_____ is rapid speciation under conditions in which there is little competition

adaptive radiation

Mass extinctions create conditions that promote ___

adaptive radiation

The appearance of an evolutionary novelty promotes __

adaptive radiation

The different finch species found on the Galápagos Islands probably arose as a result of ____

adaptive radiation

How did some stickleback populations come to live exclusively in fresh water?

Some stickleback populations became trapped in lakes that formed at the end of the last ice age

Why do some stickleback populations lack pelvic spines?

In lakes where there are no large predatory fish, there is no advantage to having pelvic spines. In lakes with dragonfly larvae, pelvic spines can be disadvantageous, allowing the predatory larvae to grab the fish.

Why did Kingsley and his team cross marine and freshwater sticklebacks?

To find the location of the gene(s) causing the difference between stickleback populations with and without spines.

What did researchers discover about the genetic mutation causing the loss of pelvic spines?

It occurred in a similar DNA region in freshwater stickleback populations all over the world. It is found in a regulatory region (a "switch") upstream of the coding region of the Pitx1 gene.

Bell and collaborators painstakingly documented a population of fossil sticklebacks from an ancient freshwater lake over a 20,000-year period. The prevalence of sticklebacks with full and reduced pelvises changed over time. Which is true?

The population of fish with pelvic spines that arrived in the lake at time B evolved a reduced pelvis over time (beginning at time C).

How do multiple lines of evidence (from the field, the fossil record, and molecular genetics) work together to illustrate stickleback evolution?

The fossil data show a pattern of evolution over long stretches of time. Data obtained by analyzing living fish in lakes show the selective pressures present in different environments. If the same morphological changes occur in the fossil record as in living populations, we might deduce that the genetic mechanism discovered in the living populations might be responsible for the changes observed in fossils. Genetic evidence reveals the precise molecular mechanism responsible for the change in pelvic structures in stickleback populations.

What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA?


What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?


What name is given to the process in which pre-mRNA is edited into mRNA?

RNA processing

The conversion of genetic information in the DNA of a gene into a protein in a particular cell is called

gene expression

Which of these indicates an enhancer region (what Dr. Kingsley called a "switch" in the regulation of the Pitx1 gene in threespine sticklebacks)?


_____ bind(s) to DNA enhancer regions


Which of these directly bind(s) to the promoter?

C and D

Which of the following is found in eukaryotic cells but not in prokaryotic cells?

membrane-enclosed organelles

Based on the evolutionary tree shown, mammals share a most recent common ancestor with which groups?

lizards and snakes, crocodiles, and birds

Which of the following is the correct sequence of events in the origin of life?
I. formation of protocells
II. synthesis of organic monomers
III. synthesis of organic polymers
IV. formation of DNA-based genetic systems


Which of the following statements supports the hypothesis of "an RNA world" on early Earth?

Some RNA molecules are important catalysts in modern cells.

Which statement about natural selection on early Earth is correct?

Natural selection could act on a population of proto-cells on early Earth, selecting for those that were stable and had self-replicating, catalytic RNA that allowed them to grow and divide to produce similar daughter proto-cells.

Which of the following is a defining characteristic that all protocells had in common?

a surrounding membrane or membrane-like structure

Which of the following steps has not yet been accomplished by scientists studying the origin of life?

formation of protocells that use DNA to direct the polymerization of amino acids

Earth probably formed _____ years ago, and the first life evolved as early as _____ years ago

4.5 billion years ago … 3.9 billion years ago

The earliest organisms were most likely ____


The following question refer to the figure below, which shows an outcrop of sedimentary rock whose strata are labeled A-D.

If x indicates the oldest fossils of two closely related species, neither of which is extinct, then their remains may be found in how many of these strata?

two strata

A paleontologist finds a new tyrannosaur in a site she is excavating, and wishes to date the fossil. What is the most likely method she will use?

She will infer the age of the fossil by dating layers of volcanic rock above and below the stratum containing the fossil.

Use the following information to answer the question.

A sediment core is removed from the floor of an inland sea. The sea has been in existence, off and on, throughout the entire time that terrestrial life has existed. Researchers wish to locate and study the terrestrial organisms fossilized in this core. The core is illustrated as a vertical column, with the top of the column representing the most recent strata and the bottom representing the time when land was first colonized by life.

4 cores hold from bottom to top, terrestrial cyanobacteria, plants and fungi, herbivorous invertebrates, and carnivorous tetrapods. Core A, cyanobacteria at the bottom and the rest near the top. Core B, elements evenly spread. Core C, first 2 at the bottom the other 2 top. Core D, all 4 near the top.

If arrows indicate locations in the column where fossils of a particular type (see key) first appear, then which core in the figure above has the most accurate arrangement of fossils?

core A # ~ * ^

Classify each event in the history of life into the appropriate eon or era.

Hadean eon- origin of Earth Archaean eon- oldest fossils of cells (prokaryotes) appear Proterozoic eon- oldest fossils of eukaryotic cells appear Paleozoic era- the Cambrian explosion, first tetrapods and insects appea Mesozoic era- dinosaurs evolve and radiate, origin of mammals Cenozoic era- humans appear, major radiation of pollinating insects

The age of fossils can sometimes be determined by radiometric dating, which is based on the constant rate of decay of radioactive isotopes. The time required for half of a radioactive isotope to decay is called the half-life of that isotope. For example, the isotope carbon-14 has a half-life of 5,730 years.
Suppose it is determined that a fossilized leaf contains 12.5% of the carbon-14 that was present when the fossil formed.
How old is the fossil? Express your answer numerically.

1.72×10^4 years

Only a very small percentage of organisms actually fossilize. Based on the information in the table below, rank the likely abundance of fossils of organisms A-E.

soft body with no skeleton × × × ×
soft body covered by hard shell ×
lives where sediment is not being deposited × ×
lives near the shore of a river or ocean × × ×
large population and long existence × × ×
small population and short existence × ×
lives where oxygen content is low × × ×
lives where oxygen content is high × ×
Rank the fossils of organisms A-E from most common to least common. If two fossils have the same commonness, overlap them.

Most common: Organism E Organism A Organism B Orgainism C Organism D Least common

If the half-life of carbon-14 is about 5,730 years, then a fossil that has one-fourth the normal proportion of carbon-14 to carbon-12 should be about how many years old?


How many half-lives should have elapsed if 6.25% of the parent isotope remains in a fossil at the time of analysis?


If the half-life of carbon-14 is about 5,730 years, then a fossil that has 75% of the normal proportion of carbon-14 to carbon-12 should be about how many years old?


Radiometric dating __

allows us to indirectly date fossils up to billions of years old based on minerals in surrounding volcanic strata

Why are fossils considered to be an incomplete record of evolution?

The fossil record is biased for organisms that had hard shells and skeletons

Fossilized stromatolites

resemble structures formed by bacterial communities that are found today in some warm, shallow, salty bays

Earth is very old, and it can be difficult to visualize where key events in the history of life occurred against this backdrop of "deep time." One common way to represent geologic time uses the analogy of a one-hour countdown timer. The timer starts from the top at Earth’s origin (4.6 billion years ago) and moves clockwise to the present, making one full circle. In this analogy, one hour represents 4.6 billion years, one minute represents roughly 76.67 million years, and one second represents roughly 1.28 million years. (Open Hint 1 for an explanation of how these calculations are done.)
A rough outline of a geological time clock compared to a speedometer-like dial. A circle with a center labeled "Billions of years ago" and an arrow wrapping clockwise from an "Origin of solar system and Earth" leader line to a "Present" leader line. The "origin" line is just to the right of the "present" line. The circle is broken up into six unequal portions: (1) from the origin (4.6 bya) to 4 bya, (2) from 4 bya to 2.5 bya, (3) from 2.5 bya to .6 bya, (4) from .6 bya to .26 bya, (5) from .26 bya to .1 bya, and (6) from .1 bya to present time. Next to this circle is a separate circle with 12 hash marks labeled clockwise in increments of 15 from 60 at 12 o’clock to 5 at 11 o’clock. A dial hand points to 30.

Using the analogy of a one-hour countdown timer, what is Earth’s age at 30 minutes ago?

2.3 billion years old

Use the figure to determine which eon has lasted the longest to date.


Surrounding the clock are colored bars denoting the start and duration of major events in Earth’s history. What major events mark the Proterozoic eon?

Origin of animals, origin of multicellular eukaryotes, origin of single-celled eukaryotes

Many present-day animal phyla appeared suddenly in fossils formed 535-525 million years ago, during the Paleozoic era of the Phanerozoic eon. This period is referred to as the Cambrian explosion. Does this period mark the beginning of animal life?

No, animals originate about 700 million years ago during the proterozoic eon

Use the figure to complete the paragraph about human origins.
Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Not all terms will be used.

Humans first appeared during the Cenozoic era of the Phanerozoic eon. While the exact date of human origin cannot be determined from the figure, you can see from the figure that humans have been around for a very short time compared to other animals. On a one-hour time scale in which Earth originated 60 minutes ago, animals appeared about 9 minutes ago, and humans appeared about 0.2 seconds ago.

The atmosphere of early Earth probably contained no O2 until the emergence of organisms that ___

used water as an electron source for photosynthesis

What was the "oxygen revolution," which took place 2.3 billion years ago?

The "oxygen revolution" was the rapid increase in atmospheric oxygen that took place 2.3 billion years ago, dooming many prokaryotic groups.

The oxygen revolution changed Earth’s environment dramatically. Which of the following took advantage of the presence of free oxygen in the oceans and atmosphere?

the evolution of cellular respiration, which used oxygen to help harvest energy from organic molecules

In the origin of the eukaryotes, endosymbiosis

most likely began with a heterotrophic endosymbiont entering the cell as undigested prey or as an internal parasite.

During the origin of the eukaryotic cell, it is thought that engulfed bacteria

did not initially have a mutually beneficial relationship with their hosts, but later evolved one.

Which of the cells shown in the figure are eukaryotic cells?

5, 6, and 7

If the mitochondria and chloroplasts in eukaryotic cells resulted from endosymbiosis with prokaryotes, what feature(s) might we expect these organelles to contain?

a cell membrane, DNA, and ribosomes

Which of the following characteristics are expected in the first animals to have colonized land?

I) They were probably herbivores (ate photosynthesizers).
II) Animals had four appendages.
III) Animals had the ability to resist dehydration.
IV) Animals had lobe-finned fishes as ancestors.
V) Invertebrates

I, III, and V

Place the key events in evolutionary history in their correct sequence. Be sure to read Chapter 25.3, and watch my mini-lecture on the History of Life on Earth before answering this question. You will only have 3 tries to get it all right. Important point to consider: Which comes first among the prokayotes: aerobic respiration or photosynthesis? Why? Which comes first among the eukaryotes: aerobic respiration or photosynthesis? Why?

1. (earliest organisms) anaerobic heterotrophic prokaryote 2. autotrophic prokaryotes 3. aerobic heterotrophic prokaryotes 4. aerobic heterotrophic eukaryotes 5. photosynthetic eukaryotes 6. multicellular eukaryotes 7. Cambrian explosion 8. terrestrial plants and fungi form symbioses 9. terrestrial invertebrate animals 10. (most recent organisms) terrestrial tetrapods

We are living during the _____era


Life arose during the ____


The Cenozoic era began approximately _____ million years ago


_____ were the dominant vertebrate life form during the Mesozoic era


How does continental drift explain the unique Australian fauna?

The separation of the southern continents from Gondwana formed a geographically isolated island of marsupials

How does continental drift affect living organisms?

It causes climate change, which puts selective pressure on organisms. It causes changes in habitats, such as when large amounts of shallow marine habitat were lost in the formation of Pangaea. It may cause an increase or decrease in competition among different species. It happens so slowly that it does not affect living organisms. All but one of these are correct. Answer: All but one of these are correct

96% of marine animal species became extinct in the Permian mass extinction at the end of the Paleozoic, 252 million years ago.
Why does the blue curve show only a 50% drop at that time?

Families typically contain many species, so the percentage of families that became extinct is lower than the percentage of species that became extinct.

According to the theory of seafloor spreading, oceanic islands, such as the Hawaiian Islands, form as oceanic crustal plates move over a stationary "hot spot" in the mantle. Currently, the big island of Hawaii is thought to be over a hot spot, which is why it is the only one of the seven large islands that has active volcanoes. What should be true of the island of Hawaii?

I) Scientists in search of ongoing speciation events are more likely to find them here than on the other six large islands.
II) Its species should be more closely related to those of nearer islands than to those of farther islands.
III) It should have a rich fossil record of terrestrial organisms.
IV) It should have species that are not found anywhere else on Earth.
V) On average, it should have fewer species per-unit surface area than the other six islands.

I, II, IV and V

Upon being formed, oceanic islands, such as the Hawaiian Islands, should feature what characteristic, leading to which phenomenon?

a variety of empty ecological niches, leading to adaptive radiation

The figure shows eyes found among living molluscs, ranging from a patch of pigmented cells in a limpet to a complex, image-forming eye in a squid. Is it possible that a structure as complex as an image-forming eye evolved by natural selection?

Yes, if the photoreceptor cells and simple eyes that preceded it were useful to the animals in which they arose.

Insect wings may have begun to evolve as lateral extensions of the body that were used as heat dissipaters for thermoregulation. When they had become sufficiently large, these extensions became useful for gliding through the air. Additional selection refined them as flight-producing wings. If this hypothesis is correct, modern insect wings would be an example of __

an exaptation

If one organ is an exaptation of another organ, then what must be true of these two organs?

They are both homologus organs

Evolution works by ____

"tinkering" with existing structures

What was the main goal of the Human Genome Project (HGP)?

to map all the human genes and determine the nucleotide sequence of the entire human genome

Current analysis indicates that less than 2% of the human genome codes for proteins. Based on the systems approach employed by the ENCODE project, what percentage of the genome is estimated to be transcribed at some point in at least one cell type?

about 75%

Why is the outdated term "junk DNA" a misnomer for noncoding regions of the human genome?

The conservation of "junk DNA" sequences in diverse genomes suggests that they have important functions.

Part complete
How do transposons differ from retrotransposons?

Transposons move by means of a DNA intermediate, whereas retrotransposons move by means of an RNA intermediate. Transposons may or may not leave a copy behind at the original site, whereas retrotransposons always leave a copy behind at the original site.

Which of the following can be duplicated in a genome?

DNA sequences, chromosomes, or sets of chromosomes

Which of the following statements correctly describes one characteristic of a multigene family?

A multigene family includes genes whose sequences are very similar and that probably arose by duplication.

When gene duplication occurs to its ultimate extent by doubling all genes in a genome, which of the following results has occurred?

creation of a polyploid

How has gene duplication played a critical role in evolution?

It produces redundant copies of existing genes, which are then free to mutate and adopt new functions

Part complete
A current view of how the human and chimpanzee can share most of their nucleotide sequences yet exhibit significant phenotypic differences is that many of the most important sequence differences alter _____

regulatory sequences

What is the goal of comparative genomic studies?

to identify genes that are important for evolution of a particular species to study how genomes evolve to identify homologues in model organisms for genes involved in human disease to study genetic variation within a species or a population. answer= all of the above

Biologists now routinely test for homology between genes in different species. If genes are determined to be homologous, how are they related to each other?

by descent from a common ancestor

Which of the following statements about descent with modification is false?

All similarities between organisms result from descent from a common ancestor.

Which of the following taxonomic categories contains all the others listed here?

Class contains order, species, genus, family

If organisms A, B, and C belong to the same class but to different orders and if organisms C, D, and E belong to the same order but to different families, which of the following pairs of organisms would be expected to show the greatest degree of structural homology?

D and E

What does the left most point of this figure represent?

The species that is a common ancestor to all species shown on the tree

Which numbered point on the tree represents the most recent common ancestry of crocodiles, dinosaurs and birds?


According to this phylogenetic tree, which type of organism is most closely related to saurichian dinosaurs?


what is represented along the x axis of this phylogenetic tree?


Over time the DNA sequences of organisms become more and more different form the DNA sequences of their ancestors, if you were to compare DNA sequences of the six organisms shown here, which group of organism would have the most different DNA sequences from the other five?

lizards and snakes

Which branch point represents the most recent common ancestor of all bears?

Branch point 1

Which branch point represents the most recent common ancestor of the sloth bear and the spectacled bear?

Branch point 2

Which branch point represents the most recent common ancestor of the Asian black bear and the brown bear?

Branch point 4

Which species is the basal taxon in this tree?

the giant panda

Identify the sister taxon to the polar bear.

The brown bear

According to this tree, is the sun bear more closely related to the sloth bear or the polar bear?

The polar bear

following groups of species is a monophyletic group, or clade?

sun bear, Asian black bear, American black bear, ancestral species 5, ancestral species 6

A study published in 2000 sequenced part of the mitochondrial cytochrome b gene from 61 brown bears from two sites in Alaska. One population of brown bears lives on the coastal mainland of Alaska, while a separate population lives on the ABC islands in southeastern Alaska.Mainland and ABC brown bears differ by 11 fixed nucleotide substitutions in the cytochrome b gene. This suggests that the two brown bear populations represent genetically unique clades.The researchers compared the cytochrome b sequences of the two clades of Alaskan brown bears to those of 55 polar bears. The analysis showed that polar bears and ABC brown bears differ at only three nucleotides in this gene, whereas polar bears and mainland brown bears had more differences.
Based on the results of the 2000 study, how should the portion of the tree extending from branch point 7 be altered?

—Mainland brown -<ABC brown bear Polar bear

Based on the revised branch of the tree, what kind of group do brown bears plus ancestral species 7 represent?

a paraphyletic group

Biologists consider phylogenies like this to be __


Which taxa on this phylogeny are basal, the first taxa to diverge from the ancestors of elephants? Check all that apply.

Sirenia and Hyracoidea

Which taxa are extant?

Sirenia, Loxodonta, Elephas, Hyracoidea

Based on the tree below, which statement is not correct?

Lizards are more closely related to salamanders than to humans.

In the phylogenetic trees, numbers represent species, and the same species are shown in both trees. Which two species are represented as sister species in Tree 2 but are not shown as sister species in Tree 1?

3 and 4

Which of the following trees, if any, depicts the same relationship among species as shown above?


Animals that possess homologous structures probably __

evolved from the same ancestor

Consider the figure, above, showing bat and bird forelimbs, and the phylogenetic relationship between bats and birds. The phylogeny indicates the lineage in which limbs and wings evolved.

In a comparison of birds and mammals, having four limbs is _____

a shared ancestral character

Consider the figure, above, showing bat and bird forelimbs, and the phylogenetic relationship between bats and birds. The phylogeny indicates the lineage in which limbs and wings evolved.

In a comparison of birds and bats, having wings capable of flight is

an example of analogy rather than homology.

The common ancestors of birds and mammals were very early (stem) reptiles, which almost certainly possessed three-chambered hearts (two atria, one ventricle). Birds and mammals, however, are alike in having four-chambered hearts (two atria, two ventricles). The four-chambered hearts of birds and mammals are best described as ________

structural analogies

By definition a clade is __


Refer to the figure. Which of the following forms a monophyletic group?

E, F, and G

This figure shows a phylogenetic tree of birds and their close relatives. Identify the monophyletic taxon.

Birds and dinosaurs and their common ancestor

Giardia intestinalis can cause disease in several different mammalian species, including humans. Giardia organisms (G. intestinalis) that infect humans are similar morphologically to those that infect other mammals, thus they have been considered a single species. However, G. intestinalis has been divided into different subgroups based on their host and a few other characteristics.

In 1999, a DNA sequence comparison study tested the hypothesis that these subgroups actually constitute different species. The following phylogenetic tree was constructed from the sequence comparison of rRNA from several subgroups of G. intestinalis and a few other morphologically distinct species of Giardia. The researchers concluded that the subgroups of Giardia are sufficiently different from one another genetically that they could be considered different species. (T. Monis, et al. 1999. Molecular systematics of the parasitic protozoan Giardia intestinalis. Mol. Biol. Evol. 16[9]:1135-44.)

A tree divides; the first branch ends in Giardia muris. The second branch divides again. The left side there divides, moving outward from the divide, into species C, B, and A. The right side divides near the end into specie D and Giardia Microti. Species A through D are labeled Giardia Intestinalis, Subgroups A-D.
According to the phylogenetic tree in the figure above, G. intestinalis constitutes a ________ group


Giardia intestinalis can cause disease in several different mammalian species, including humans. Giardia organisms (G. intestinalis) that infect humans are similar morphologically to those that infect other mammals, thus they have been considered a single species. However, G. intestinalis has been divided into different subgroups based on their host and a few other characteristics.

In 1999, a DNA sequence comparison study tested the hypothesis that these subgroups actually constitute different species. The following phylogenetic tree was constructed from the sequence comparison of rRNA from several subgroups of G. intestinalis and a few other morphologically distinct species of Giardia. The researchers concluded that the subgroups of Giardia are sufficiently different from one another genetically that they could be considered different species. (T. Monis, et al. 1999. Molecular systematics of the parasitic protozoan Giardia intestinalis. Mol. Biol. Evol. 16[9]:1135-44.)

A tree divides; the first branch ends in Giardia muris. The second branch divides again. The left side there divides, moving outward from the divide, into species C, B, and A. The right side divides near the end into specie D and Giardia Microti. Species A through D are labeled Giardia Intestinalis, Subgroups A-D.

By examining the phylogenetic tree diagrammed in the figure above, what conclusion can you draw about the species G. microti?

It is a part of a monophyletic group that also includes G. intestinalis

Rattlesnakes (like turtles) are reptiles, yet they do not have four limbs. In fact, they have no apparent limbs. What does this suggest?

The presence or absence of four limbs, on its own, could be misleading when considering the evolutionary relationships of rattlesnakes

Suppose that a phylogenetic tree were constructed using the data shown in this table. Mosses represent the outgroup. What would the resulting tree suggest?

Cherries and peas are each other’s closest relatives

Based on the character table in Part B, which of the following statements about shared derived characters in plants is correct?

Seeds are a shared derived character of pines, cherries, and peas.

In this phylogeny, the homologous traits that define the clade at branch points 2, 3 and 6 are identified to the left of the branch point. The clades are named in the bars to the right of the phylogeny.

Based on the homologous traits included on this phylogeny, what is a shared derived trait of the bird clade?


Based on the traits included on the phylogeny, what is a shared ancestral trait of the amniote clade?

Digit-bearing limbs

Fossil evidence indicates that some dinosaurs had feathers. If birds are indeed descended from dinosaurs, feathers are what kind of character

shared ancestral character

Given that phylogenies are based on shared derived characteristics, which of the following traits is useful in generating a phylogeny of species W, X, Y, and Z?

Species W- T1 A, T2 A, T3 A
Species X- T1 A, T2 A, T3 B
Species Y- T1 A, T2 B, T3 C
Species Z- T1 A, T2 B, T3 D

Trait 2

If you were using cladistics to build a phylogenetic tree of cats, which of the following would be the best outgroup?


Phylogenetic trees constructed from evidence from molecular systematics are based on similarities in _____

Mutations to homolgus genes

Why do researchers use rRNA in investigations of relationships between taxa that diverged hundreds of millions of years ago?

DNA coding for rRNA changes relatively slowly.

Eukaryotes that are not closely related and that do not share many anatomical similarities can still be placed together on the same phylogenetic tree by comparing their ___

homologous genes that are highly conserved

The lakes of northern Minnesota are home to many similar species of damselflies of the genus Enallagma. These species have apparently undergone speciation from ancestral stock since the last glacial retreat about 10 thousand years ago. Sequencing which of the following would probably be most useful in sorting out evolutionary relationships among these closely related species?

mitochondrial DNA

What process actually increases the number of genes in an organism’s genome?

gene duplication

Molecular clocks are based on the idea that __

on average neutral mutations arise at a constant rate

Which of the following would, if it had acted upon a gene, prevent this gene from acting as a reliable molecular clock?

natural selection

Use the graph to estimate the divergence time for a mammal with a total of 30 mutations in the seven proteins.

50 million years

Use this phylogenetic tree and your knowledge of cladistics to determine the relationships between these species.
Rank the species from most closely related to horseflies to most distantly related to horseflies. If two species are equally close in their relatedness to horseflies, overlap them.

Most closely related to horseflies Flea Human body louse and Katydid Mayfly and Dragonfly Silverfish Most distantly related to horseflies

Imagine that you are studying alien life-forms discovered on a distant planet. While geneticists are working out the genetic code of these organisms, you are asked to construct a phylogenetic tree based on four morphological features, or characters: presence or absence of a spring tail, presence or absence of a grasping hand, presence or absence of a second tail, and number of eyes. The organisms have been divided into five groups based on these characters.
The figure shows five stalk-eyed aliens. The first alien is bluish-green, and it has a big head, a spring tail attached to the bottom of the head, and 4 eyes attached to the top of the head. The second alien is dirty green, and it has a big head, two spring tails attached to the bottom of the head with one of the tails having a grasping hand, and 4 eyes attached to the top of the head. The third alien is light green, and it has a big head, a tail stalk attached to the bottom of the head, and three eyes attached to the top of the head. The fourth alien is purple, and it has a big head, two spring tails attached to the bottom of the head, and four eyes attached to the top of the head. The fifth alien is brown, and it has a big head, a spring tail attached to the bottom of the head, and 3 eyes attached to the top of the head.

If we assume the alien with a tail stalk is an outgroup, what is the most likely phylogenetic tree based on these shared derived characters? When did these characters appear during the aliens’ evolutionary history?
Drag the aliens and shared derived characters to their appropriate locations on this phylogenetic tree. Use only the blue labels for the blue targets and the white labels for the white targets.

a. Spring tail b. fourth eye c. second tail d. grasping hand e. three eyes and straight tail f. three eyes and spring tail g. four eyes and spring tail h. four eyes and two spring tails i. four eyes spring tail and limb

Part C – Choosing the most parsimonious treePart complete
The geneticists studying the alien organisms have deciphered their genetic code. For familiarity, they have used A, C, G, and T to indicate the bases in this code.
A comparable genetic sequence in each alien has been identified in the genes that code for eye growth. This genetic sequence has allowed the aliens to be divided into six groups, with the single-tail, three-eye group split in half. The geneticists also studied several outgroup species (not shown) to compile a likely ancestral DNA sequence. From this information, they have constructed four possible phylogenetic trees.
Based on this genetic information, which phylogenetic tree is most parsimonious?

phylogenetic tree III

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