Question 1

In the absence of purifying and positive selection, the ratio of the rate of synonymous substitutions to the rate of nonsynonymous substitutions should be near

Accepted Answer

The ratio of the rate of synonymous substitutions to the rate of nonsynonymous substitutions is known as dS/dN. In the absence of purifying and positive selection, dS/dN should be near 1, indicating that synonymous and nonsynonymous substitutions occur at equal rates. This is because there is no pressure to maintain or change the amino acid sequence of a protein, so changes in either type of substitution are largely neutral.

Question 2

Which statement about pseudogenes is false?

Accepted Answer

Pseudogenes are nonfunctional copies of genes that have undergone mutations and are no longer able to produce a functional protein. Therefore, choice D, which states that they are functional copies of genes, is false. Choices A and B are true, as pseudogenes are indeed nonfunctional copies of genes that can evolve faster than synonymous substitutions. Choice C is generally false, as pseudogenes generally evolve slower than nonsynonymous substitutions due to the lack of selective pressure. Choice E is true, as pseudogenes can potentially regain function through the acquisition of beneficial mutations, becoming functional paralogs.

Question 3

Researchers suspect that the gene FOXP2, which is involved in speech and cognition, has been under positive selection in the human lineage.Which of the following would provide the strongest support for such a claim?

Accepted Answer

A higher rate of nonsynonymous substitutions (changes that alter the encoded protein) compared to synonymous substitutions (changes that do not alter the encoded protein) would suggest that the FOXP2 gene has been undergoing positive selection in humans, as this would indicate that the changes are beneficial and have been favored by natural selection.

Question 4

The genes that code for the enzyme lysozyme from a number of organisms whose diets comprise mostly leaves and grass were sequenced.Comparisons of the gene sequences revealed that

Accepted Answer

The answer of The genes that code for the enzyme...

Question 5

Which general principle of molecular evolution can you most reasonably infer?

Accepted Answer

The answer of Which general principle of molecular evolution can...

Question 6

Two species of rodents that diverged 15 million years ago have accumulated an estimated 20 nucleotide differences in a gene.Both of these rodents have one generation per year.Suppose sequence analysis of offspring and parents shows that the actual total mutation rate is 1.5 per million generations.Given this information and assuming that all mutations are either deleterious or neutral, approximately _______ of mutations are neutral.

Accepted Answer

To find the proportion of neutral mutations, we first need to estimate the total number of generations that have passed since the two rodent species diverged. Since they have one generation per year, 15 million years ago would correspond to 15 million generations. Given that there are now 20 nucleotide differences between the species, this suggests an average substitution rate of 20/15 million = 1.33 x 10^-6 substitutions per site per generation.
Assuming that all substitutions are either deleterious or neutral, we can estimate the proportion of neutral mutations as the ratio of neutral substitutions to total substitutions. Since the actual total mutation rate is 1.5 per million generations, we would expect 1.5 x 1.33 x 10^-6 = 1.995 x 10^-6 substitutions per site per generation. Of these, approximately 20/2 = 10 substitutions are expected to be neutral (assuming equal rates of neutral and deleterious substitutions). Therefore, the proportion of neutral substitutions is approximately 10/1.995 x 10^-6 = 0.005, or 0.5%.

Question 7

Suppose the size of a population of crickets is 1,500.According to the theory that neutral variants accumulate through genetic drift, what is the probability that a newly arisen neutral mutation will become fixed in this population?

Accepted Answer

The answer of Suppose the size of a population of...

Question 8

Which statement about lysozymes is false?

Accepted Answer

Lysozymes are not exclusively found in foregut fermenters. They are also present in other animals, including humans.

Question 9

Which animals are foregut fermenters?

Accepted Answer

Foregut fermenters include ruminants like cattle, which have a specialized stomach for fermentation before digestion, and some non-ruminants like langurs. Lemurs are not foregut fermenters; they have a different digestive strategy.

Question 10

Mutations in the third position of codons are the least likely to affect the amino acid sequence.Mutations in the second position are most likely to change the amino acid sequence, whereas first-position mutations are intermediate.Based on what you know about molecular evolution, predict the relative rates of evolution for first-, second-, and third-position codon nucleotides, from least likely to most likely.

Accepted Answer

Third-position mutations are the most likely to be silent or synonymous, not affecting the amino acid sequence, and thus can accumulate at a higher rate. First-position mutations have an intermediate effect, while second-position mutations are most likely to alter the amino acid, being more subject to selective pressure and evolving more slowly.

Question 11

The central hypothesis of the neutral theory asserts that

Accepted Answer

The neutral theory posits that most genetic variation is due to random drift of mutant alleles that are selectively neutral, meaning they do not affect an organism's fitness.

Question 12

Suppose that the size of a population of midges is 20 million and that the mutation rate of a neutral gene is 1.5 per million.How many new mutations of this gene should appear in the population per generation?

Accepted Answer

The answer of Suppose that the size of a population...

Question 13

A DNA substitution does not change the amino acid sequence of the protein.This change is thus a _______ substitution.

Accepted Answer

A silent substitution is a type of point mutation that does not alter the amino acid sequence of the polypeptide chain. The substitution occurs in the DNA coding sequence, but the resulting protein remains unchanged, as the new codon codes for the same amino acid as the original codon. Silent substitutions are also called synonymous substitutions.

Question 14

Consider the great diversity of genome size among organisms.As genome size increases, the relative proportion of noncoding DNA

Accepted Answer

As genome size increases, the proportion of noncoding DNA increases. This is because the coding regions of DNA (genes) only make up a small portion of the whole genome, while noncoding regions such as introns, regulatory regions, and repetitive elements increase as the size of the genome increases. Therefore, the relative proportion of noncoding DNA steadily increases as genome size increases.

Question 15

Which statement about mutations is false?

Accepted Answer

Nonsynonymous mutations can be deleterious, beneficial, or neutral depending on the specific amino acid change and its effect on protein function.

Question 16

A missense substitution is the same as a _______ substitution.

Accepted Answer

A missense substitution is a type of nonsynonymous substitution, where a single nucleotide change in the DNA sequence results in a different amino acid being incorporated into the protein. Silent substitutions (A) and synonymous substitutions (B) do not result in an amino acid change, while coincident (D) and parallel (E) are not relevant terms in this context.

Question 17

In a eukaryote, one would expect to find the lowest rate of nonsynonymous nucleotide substitutions in an

Accepted Answer

Nonsynonymous substitutions result in changes to the amino acid sequence of a protein, which can affect its function. Exons of protein-coding genes are under strong selective pressure to maintain the correct amino acid sequence, as mutations that affect protein function can be deleterious. In contrast, introns and pseudogenes are not under the same selective pressure, so nonsynonymous substitutions are expected to occur more frequently in these regions. Therefore, the lowest rate of nonsynonymous substitutions is expected in the exons of protein-coding genes.

Question 18

Which observation is contrary to the neutral theory of molecular evolution?

Accepted Answer

The neutral theory of molecular evolution posits that most evolutionary changes at the molecular level are the result of genetic drift acting on neutral mutations (those that do not affect an organism's fitness). Therefore, the statement that variants within populations that arise because of genetic drift are always advantageous (E) is contrary to this theory, as it suggests all such variants confer an advantage, which contradicts the neutral theory's premise that most are neutral in terms of fitness.

Question 19

Which statement about synonymous substitutions is false?

Accepted Answer

Synonymous substitutions do not change the amino acid sequence of the protein, which makes statement E false.

Question 20

Refer to the table  Consider the codon UUA.Which of the following codons is representative of one or more synonymous substitution(s)?

Accepted Answer

The answer of Refer to the table  Consider the...

Quiz 23: Evolution of Genes and Genomes