Question 1

Researchers obtained the data depicted here by sampling human blood containing HIV and then isolating and sequencing genes within the human immunodeficiency virus's DNA.What does the line and shaded area that intersect the x-axis represent? 
A)an index of natural selection on the HIV genes studied
B)an index of mutations within gene regions of HIV that are unrelated to the success of the virus (such as how virulent it is or how well it reproduces within its human hosts)
C)a measurement of changes between HIV gene sequences,specifically on genes important for the replication,reproduction,and spreading of the virus
D)a prediction of when HIV first infected humans,based on the theory that neutral DNA mutations to non-protein coding sections of the HIV genome have accumulated in a consistent manner over time.

Accepted Answer

The line and shaded area that intersect the x-axis represent a prediction of when HIV first infected humans, based on the theory that neutral DNA mutations to non-protein coding sections of the HIV genome have accumulated in a consistent manner over time. These mutations can be used as a molecular clock to estimate the time of origin of the virus.

Question 2

Cladograms (a type of phylogenetic tree)constructed from evidence from molecular systematics are based on similarities in
A)morphology.
B)the pattern of embryological development.
C)biochemical pathways.
D)mutations to homologous genes.

Accepted Answer

Cladograms constructed from evidence from molecular systematics are based on mutations to homologous genes. This is because molecular systematics is the study of evolutionary relationships based on molecular evidence, such as DNA or amino acid sequences, and these sequences are used to identify similarities and differences, which can be used to construct cladograms.

Question 3

According to the principle of maximum parsimony,
A)phylogenies based in DNA require the most base changes between taxa.
B)the preferred tree is the one that minimizes the amount of evolutionary change.
C)in the case of trees based on morphology,a parsimonious tree requires the most changes.
D)a large number of trees should be examined.

Accepted Answer

The principle of maximum parsimony states that the preferred tree is the one that requires the least amount of evolutionary change. This means that the tree that requires the fewest number of genetic or morphological changes is the most parsimonious and therefore, the most likely to be accurate. Therefore, choice B is the correct answer.

Question 4

When using a cladistic approach to systematics,which of the following is considered most important for classification?
A)shared primitive characters
B)analogous primitive characters
C)shared derived characters
D)the number of homoplasies

Accepted Answer

In cladistics, classification is based on shared derived characters that are unique to a particular clade and not found in more distantly related organisms. Shared primitive characters (A) are ancestral traits that are present in a wide range of organisms and therefore not useful for distinguishing between closely related species. Analogous primitive characters (B) are traits that have similar functions but are not derived from a common ancestor and therefore not informative for establishing evolutionary relationships. The number of homoplasies (D), or instances of convergence, can be used to evaluate the reliability of a particular phylogenetic hypothesis, but it is not the primary criterion for classification.

Question 5

When it acts upon a gene,which of the following processes consequently makes that gene an accurate molecular clock?
A)transcription
B)directional natural selection
C)mutation
D)proofreading
E)reverse transcription

Accepted Answer

Mutations in a gene can accumulate over time and can be used as a measure of evolutionary divergence, making the gene an accurate molecular clock. However, not all mutations in a gene will be neutral or evolve at a constant rate, so careful selection of the appropriate gene and type of mutation is necessary for accurate molecular clock analysis.

Question 6

Neutral theory proposes that
A)molecular clocks are more reliable when DNA mutations occur on the nitrogenous bases,thymine (T)and adenine (A).
B)most mutations of highly conserved DNA sequences should have no functional effect.
C)DNA is less susceptible to mutation when it codes for amino acid sequences whose side groups (or R groups)have a neutral pH.
D)DNA is less susceptible to mutation when it codes for amino acid sequences whose side groups (or R groups)have a neutral electrical charge.
E)a significant proportion of mutations are not acted upon by natural selection.

Accepted Answer

Neutral theory proposes that a significant proportion of mutations are not acted upon by natural selection, and therefore accumulate in populations without affecting their fitness. This is in contrast to the traditional view of evolution, which assumes that all mutations are subject to selection and therefore only those that provide a fitness advantage are passed on to future generations. The neutral theory has been supported by studies of molecular evolution, which have shown that many genetic changes in DNA sequences have no effect on the phenotype and are therefore neutral with respect to selection.

Question 7

A phylogenetic tree constructed using sequence differences in mitochondrial DNA would be most valid for discerning the evolutionary relatedness of
A)archaeans and bacteria.
B)fungi and animals.
C)chimpanzees and humans.
D)sharks and dolphins.

Accepted Answer

Mitochondrial DNA is inherited maternally and is highly conserved, making it an ideal marker for studying evolutionary relationships within closely related species. Thus, a phylogenetic tree constructed using sequence differences in mitochondrial DNA would be most valid for discerning the evolutionary relatedness of chimpanzees and humans, who are closely related primates. It would not be as useful for studying distantly related groups such as archaeans and bacteria, fungi and animals, or sharks and dolphins.

Question 8

You discover a fossil with feathers on forelimbs,short hind limbs,and teeth.You conclude that this organism appears early on a phylogenetic tree for which group of organisms?
A)reptiles
B)birds
C)mammals
D)snakes

Accepted Answer

The presence of feathers suggests that the organism is a bird or an early bird ancestor. The short hind limbs and teeth suggest that it is not a modern bird but an earlier ancestor. The combination of these traits suggests that the organism is on an early branch of the bird lineage.

Question 9

There is some evidence that extinct reptiles called cynodonts,which arose about 260 million years ago,may have had whisker-like hairs around their mouths.If this is true,then what can be properly said of hair?
A)It is a shared derived character of mammals,even if cynodonts continue to be classified as reptiles.
B)It is a shared derived character of the amniote clade and not of the mammal clade.
C)It is a shared ancestral character of the amniote clade,but only if cynodonts are reclassified as mammals.
D)It is a shared derived character of the mammals,but only if cynodonts are reclassified as mammals.

Accepted Answer

The answer of There is some evidence that extinct reptiles...

Question 10

Which of the following is true of all horizontally oriented phylogenetic trees,in which time advances to the right?
A)Each branch point represents a point in absolute time.
B)Organisms represented at the base of such trees are descendants of those represented at higher levels.
C)The fewer branch points that occur between two taxa,the more divergent their DNA sequences should be.
D)The common ancestor represented by the rightmost branch point existed more recently in time than the common ancestors represented at branch points located to the left.

Accepted Answer

In horizontally oriented phylogenetic trees, time advances to the right. Therefore, the common ancestors represented by the rightmost branch point existed more recently in time than the common ancestors represented at branch points located to the left. Thus, option D is correct. Option A is incorrect because not all phylogenetic trees may represent timepoints; some may represent evolutionary relationships. Option B may be true for some trees, but not necessarily for all horizontally oriented trees. Option C is not a generalization that holds true for all trees; the number of branch points could be affected by factors such as incomplete sampling, horizontal gene transfer, and convergence.

Question 11

A phylogenetic tree shows that birds and crocodiles share many features.A hypothesis based on this tree predicts that these features are present in a common ancestor.Which of these predicted traits is supported by fossil evidence?
A)four-chambered heart
B)singing for territory
C)eggs and nests
D)singing to attract mates

Accepted Answer

Fossil evidence supports that both birds and crocodiles share the trait of laying eggs and building nests, which can be traced back to their common ancestors. This is a trait that has been observed in fossils of ancient reptiles, indicating its presence in the lineage leading to both modern birds and crocodiles.

Question 12

Which of the following are problematic when the goal is to construct phylogenies that accurately reflect evolutionary history?
A)polyphyletic taxa
B)paraphyletic taxa
C)monophyletic taxa
D)polyphyletic and paraphyletic taxa

Accepted Answer

Polyphyletic and paraphyletic taxa are problematic when constructing phylogenies as they do not accurately reflect evolutionary history. A polyphyletic taxon includes groups with different ancestors, while a paraphyletic taxon includes only some but not all descendants of a common ancestor. These types of taxa can lead to incorrect evolutionary relationships and should be avoided in phylogenetic analyses. Monophyletic taxa, on the other hand, include all descendants of a common ancestor and are preferred when constructing accurate phylogenies.

Question 13

The observation that genetic mutations in the genome appear to accumulate at constant rates across a wide diversity of taxa led to the development of
A)phylogenetic analysis.
B)cladistics.
C)molecular clocks.
D)maximum parsimony.

Accepted Answer

The observation of constant rates of genetic mutations across taxa led to the development of molecular clocks, which rely on the assumption that mutations accumulate in a clock-like fashion and can be used to estimate evolutionary time scales. Phylogenetic analysis, cladistics, and maximum parsimony are methods for inferring evolutionary relationships but are not directly related to the observation of molecular clocks.

Question 14

Researchers obtained the data depicted in this figure by sampling human blood containing HIV and then isolating and sequencing genes within the human immunodeficiency virus's DNA .What does the y-axis represent? 
A)an index of natural selection on the HIV genes studied
B)an index of mutations within gene regions of HIV that are unrelated to the success of the virus (such as how virulent it is or how well it reproduces within its human hosts)
C)a measurement of changes between HIV gene sequences,specifically on genes important for the replication,reproduction,and spreading of the virus
D)an index of time since the first human HIV infection occurred

Accepted Answer

The answer of Researchers obtained the data depicted in this...

Question 15

How does a molecular clock measure time?
A)by observing that some genes and other regions of genomes appear to evolve at different rates
B)by detecting gene irregularities that result from natural selection
C)by counting the number of nucleotide substitutions over a fixed period of time
D)by using few gene mutations to calibrate the clock

Accepted Answer

A molecular clock measures time by counting the number of nucleotide substitutions over a fixed period of time. The rate of nucleotide substitutions is generally constant for a given gene or region of the genome, and this rate can be used to estimate the time since two organisms diverged from a common ancestor. This approach assumes that the rate of nucleotide substitutions is approximately constant and that mutations are selectively neutral, meaning they do not confer any advantage or disadvantage to the organism.

Question 16

A shared ancestral character is
A)a character that originated in an ancestor of two taxa.
B)shared by all mammals but not found in their ancestors.
C)an evolutionary novelty unique to a clade.
D)an outgroup character.

Accepted Answer

A shared ancestral character is a character that originated in an ancestor of two taxa and is present in both. This can help to determine evolutionary relationships between different groups of organisms.

Question 17

Which kind of DNA should provide the best molecular clock for determining the evolutionary relatedness of several species whose common ancestor became extinct billions of years ago?
A)DNA coding for ribosomal RNA
B)intronic DNA belonging to a gene whose product performs a crucial function
C)paralogous DNA that has lost its function (that is,no longer codes for functional gene product)
D)mitochondrial DNA
E)exonic DNA that codes for a noncrucial part of a polypeptide

Accepted Answer

DNA coding for ribosomal RNA is highly conserved across different species due to its essential role in protein synthesis. This conservation makes it an excellent molecular clock for studying evolutionary relationships over long periods.

Question 18

Which of these would,if it (they)had acted upon a gene,prevent this gene from acting as a reliable molecular clock?
A)neutral mutations
B)genetic drift
C)mutations within introns
D)natural selection
E)most substitution mutations involving a codon's third position (of exons)

Accepted Answer

Natural selection can prevent a gene from acting as a reliable molecular clock because it can accelerate or decelerate the rate of mutations in a gene based on environmental pressures and the fitness benefits or detriments of those mutations, thus disrupting the steady, predictable rate of mutation necessary for a molecular clock.

Question 19

The most important feature that permits a gene to act as a molecular clock is
A)having a large number of base pairs.
B)having a larger proportion of exonic DNA than of intronic DNA.
C)having a reliable average rate of mutation.
D)its recent origin by a gene duplication event.
E)its being acted upon by natural selection.

Accepted Answer

A gene can act as a molecular clock only when it has a reliable average rate of mutation. This means that the gene should accumulate mutations at a constant rate over time, allowing for the estimation of time since divergence of different species or lineages. Other features such as size or origin by duplication are irrelevant for the molecular clock hypothesis. Similarly, natural selection affects the rate of substitution of different types of mutations and therefore cannot be assumed to be constant over time.

Question 20

Analisa and Mateo,two research anthropologists interested in deciphering the relatedness between four extinct primates,were studying the similarities and differences among a number of measurements of the complex structures of the jaw fragments they collected,as well as making many other morphological contrasts between other fossilized bones from dozens of collected specimens.In the lab,they noticed the lengths of the bones of the leg,particularly the femur,tibia,and fibula,were very different in all the specimens,whereas the jaw structures were nearly identical among the specimens.What should they tentatively conclude based on this evidence?
A)The four primates likely share a close common ancestor or could potentially be the same species based upon the jaw measurements.
B)The hominids with the most closely matching leg bone measurements are likely more closely related than the others,due to the importance of locomotion as an evolutionary adaptation.
C)The femur measurements are not important.
D)Because the measurements of the leg bones vary widely,it is probable that the four species are from different genera.

Accepted Answer

The fact that the jaw structures are nearly identical among the specimens suggests that they may be the same species or share a close common ancestor. The differences in leg bone measurements are not as informative for deciphering relatedness between the primates as these measurements could be influenced by factors such as differences in size or environment. Therefore, they should tentatively conclude that the primates likely share a close common ancestor or could potentially be the same species based upon the jaw measurements.

Quiz 20: Phylogeny

Researchers obtained the data depicted here by sampling human blood containing HIV and then isolating and sequencing genes within the human immunodeficiency virus's DNA.What does the line and shaded area that intersect the x-axis represent?

Cladograms (a type of phylogenetic tree) constructed from evidence from molecular systematics are based on similarities in

According to the principle of maximum parsimony,

When using a cladistic approach to systematics,which of the following is considered most important for classification?

When it acts upon a gene,which of the following processes consequently makes that gene an accurate molecular clock?

Neutral theory proposes that

A phylogenetic tree constructed using sequence differences in mitochondrial DNA would be most valid for discerning the evolutionary relatedness of

You discover a fossil with feathers on forelimbs,short hind limbs,and teeth.You conclude that this organism appears early on a phylogenetic tree for which group of organisms?

There is some evidence that extinct reptiles called cynodonts,which arose about 260 million years ago,may have had whisker-like hairs around their mouths.If this is true,then what can be properly said of hair?

Which of the following is true of all horizontally oriented phylogenetic trees,in which time advances to the right?

A phylogenetic tree shows that birds and crocodiles share many features.A hypothesis based on this tree predicts that these features are present in a common ancestor.Which of these predicted traits is supported by fossil evidence?

Which of the following are problematic when the goal is to construct phylogenies that accurately reflect evolutionary history?

The observation that genetic mutations in the genome appear to accumulate at constant rates across a wide diversity of taxa led to the development of

Researchers obtained the data depicted in this figure by sampling human blood containing HIV and then isolating and sequencing genes within the human immunodeficiency virus's DNA .What does the y-axis represent?

How does a molecular clock measure time?

A shared ancestral character is

Which kind of DNA should provide the best molecular clock for determining the evolutionary relatedness of several species whose common ancestor became extinct billions of years ago?

Which of these would,if it (they) had acted upon a gene,prevent this gene from acting as a reliable molecular clock?

The most important feature that permits a gene to act as a molecular clock is