26.5 Molecular clocks help track evolutionary

Question 1

56) Paralogous genes that have lost the function of coding for a functional gene product are
known as ʺpseudogenes.ʺ Which of these is a valid prediction regarding the fate of
pseudogenes over evolutionary time?
A) They will be preserved by natural selection.
B) They will be highly conserved.
C) They will ultimately regain their original function.
D) They will be transformed into orthologous genes.
E) They will have relatively high mutation rates.

Answer 1

E) They will have relatively high mutation rates.

Question 2

57) Theoretically, molecular clocks are to molecular phylogenies as radiometric dating is to
phylogenies that are based on the
A) fossil record.
B) geographic distribution of extant species.
C) morphological similarities among extant species.
D) amino acid sequences of homologous polypeptides.

Answer 2

A) fossil record.

Question 3

58) 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.

Answer 3

C) having a reliable average rate of mutation.

Question 4

59) Neutral theory proposes that
A) molecular clocks are more reliable when the surrounding pH is close to 7.0.
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 is not acted upon by natural selection.

Answer 4

E) a significant proportion of mutations is not acted upon by natural selection.

Question 5

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

Answer 5

B) directional natural selection

Question 6

62) Which of these would, if it 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 an exonic codonʹs 3rd position

Answer 6

D) natural selection

Question 7

63) The HIV genomeʹs reliably high rate of change permits it to serve as a molecular clock.
Which of these features is most responsible for this genomeʹs high rate of change?
A) the relatively low number of nucleotides in the genome
B) the relatively small number of genes in the genome
C) the genomeʹs ability to insert itself into the genome of the host
D) the lack of proofreading by the enzyme that converts HIVʹs RNA genome into a DNA genome

Answer 7

D) the lack of proofreading by the enzyme that converts HIVʹs RNA genome into a DNA genome

Question 8

67) Which of these is the best explanation for the relatively low level of sequence homology
observed in Intron VI?
A) Mutations that occur here are neutral; thus, are neither selected for nor against, and thereby accumulate over time.
B) Its higher mutation rate has resulted in its highly conserved nature.
C) The occurrence of molecular homoplasy explains it.
D) This intron is not actually homologous, having resulted from separate bacteriophage-induced transduction events in these five species.

Answer 8

A) Mutations that occur here are neutral; thus, are neither selected for nor against, and thereby accumulate over time.

Question 9

68) Which of these is the best explanation for Intron Iʹs relatively high sequence homology
among these five species?
A) It is the most-upstream of this geneʹs introns.
B) It was once an exon, but became intronic in the common ancestor of these five species.
C) Due to alternative gene splicing, it is often treated as an exon in these five species; as an exon, it codes for an important part of a polypeptide.
D) It has a relatively high average rate of mutation.

Answer 9

C) Due to alternative gene splicing, it is often treated as an exon in these five species; as an exon, it codes for an important part of a polypeptide.

Question 10

69) Which of these four gene parts should allow the construction of the most accurate
phylogenetic tree, assuming that this is the only part of the gene that has acted as a reliable
molecular clock?
A) Intron I
B) Exon I
C) Intron VI
D) Exon V

Answer 10

C) Intron VI