Question 1

During an individual organism's lifetime, which of these is most likely to help the organism respond properly to changes in its environment?

Accepted Answer

Changes in gene expression allow an individual organism to respond to changes in its environment during its lifetime. Microevolution and changes in allele or gene frequency occur over many generations and do not affect an individual's ability to respond to immediate changes in its environment. Average heterozygosity is a measure of genetic diversity within a population and does not necessarily impact an individual's ability to respond to environmental changes.

Question 2

Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?

Accepted Answer

During the prolonged drought on Daphne Major, the survival of the finches was strongly influenced by the depth and strength of their beaks. The birds with deeper, stronger beaks were better able to crack open the tough, dry seeds that were available during the drought, while birds with smaller, weaker beaks were less successful at obtaining food and had lower survival rates. This resulted in a shift in the distribution of beak sizes within the population, with birds that had deeper, stronger beaks being more likely to survive and reproduce. However, this does not necessarily mean that each individual bird evolved a deeper, stronger beak or that the frequency of the strong-beak alleles increased in each bird – it simply means that the distribution of beak sizes within the population changed over time. Additionally, there is no evidence to support the claim that each bird that survived produced only offspring with deeper, stronger beaks.

Question 3

The higher the proportion of loci that are "fixed" in a population, the lower is that population's

Accepted Answer

When loci are "fixed" in a population, it means that there is only one allele present at each of those loci for all individuals in the population. This results in lower nucleotide variability because there is less variation at the genetic level. It also leads to lower average heterozygosity because individuals are more likely to be homozygous for the fixed allele. Genetic polyploidy refers to the condition of having more than two sets of chromosomes and is not directly affected by the fixation of loci.

Question 4

Most invertebrates have a cluster of ten similar Hox genes, all located on the same chromosome. Most vertebrates have four such clusters of Hox genes, located on four nonhomologous chromosomes. The process that could have potentially contributed to the cluster's presence on more than one chromosome was ________.

Accepted Answer

The answer of Most invertebrates have a cluster of ten...

Question 5

If, on average, 46% of the loci in a species' gene pool are heterozygous, then the average homozygosity of the species should be

Accepted Answer

If 46% of the loci are heterozygous, then the remaining 54% must be homozygous, as the total must sum to 100%.

Question 6

Rank the following one-base point mutations (from most likely to least likely)with respect to their likelihood of affecting the structure of the corresponding polypeptide:
1)insertion mutation deep within an intron
2)substitution mutation at the third position of an exonic codon
3)substitution mutation at the second position of an exonic codon
4)deletion mutation within the first exon of the gene

Accepted Answer

A deletion mutation within the first exon (4) is most likely to affect the structure because it can cause a frameshift, altering the entire downstream amino acid sequence. A substitution at the second position of an exonic codon (3) is likely to change the amino acid, directly affecting the polypeptide structure. Substitutions at the third position of a codon (2) might not change the amino acid due to the degeneracy of the genetic code, making it less likely to affect the structure. An insertion deep within an intron (1) is least likely to affect the structure since introns are typically removed during RNA splicing and do not encode the polypeptide.

Question 7

Although each of the following has a better chance of influencing gene frequencies in small populations than in large populations, which one most consistently requires a small population as a precondition for its occurrence?

Accepted Answer

Genetic drift is the random fluctuation of gene frequencies in a population due to chance events. In small populations, chance events can have a larger impact on gene frequencies due to the smaller sample size. Therefore, genetic drift most consistently requires a small population as a precondition for its occurrence. The other options (mutation, nonrandom mating, natural selection, and gene flow) can occur in both small and large populations.

Question 8

Which statement about variation is true?

Accepted Answer

New alleles arise from changes in the nucleotide sequence of DNA, which is what nucleotide variability refers to. This is a fundamental source of genetic diversity.

Question 9

Which of the following is a true statement concerning genetic variation?

Accepted Answer

Genetic variation must be present in a population before natural selection can act on it. Without genetic variation, there would be no differences in traits for natural selection to act upon.

Answer: D
 The processes of meiosis and fertilization during sexual reproduction can result in a reduction in genetic variation, as the number of possible allele combinations is lowered. This is known as genetic drift.

Note: Choice E is false. A higher average heterozygosity indicates a greater diversity of alleles and therefore a higher level of genetic variation.

Question 10

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus

Accepted Answer

Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, the allele's frequency should not change from one generation to the next, but its representation in homozygous and heterozygous genotypes may change.

Answer: C 
 Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, this means that, at this locus, two alleles are present in equal proportions.

Answer: D 
 Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, the population itself is not evolving, but individuals within the population may be evolving.

Question 11

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.2. What is the percentage of the population that is heterozygous for this allele?

Accepted Answer

In a Hardy-Weinberg population, the frequency of two alleles A and a can be represented as p and q, respectively. Given that the frequency of allele a (q) is 0.2, the frequency of allele A (p) would be 1 - 0.2 = 0.8. The percentage of the population that is heterozygous (Aa) can be calculated using the formula 2pq. Therefore, 2 * 0.8 * 0.2 = 0.32 or 32%.

Question 12

In the formula for determining a population's genotype frequencies, the pq in the term 2pq is necessary because

Accepted Answer

The answer of In the formula for determining a population's...

Question 13

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype?

Accepted Answer

The frequency of allele A can be calculated as 1 - 0.1 = 0.9. In a Hardy-Weinberg population, the frequency of the AA genotype is given by p^2, where p is the frequency of allele A. Therefore, the frequency of AA individuals is 0.9^2 = 0.81.

Question 14

A trend toward the decrease in the size of plants on the slopes of mountains as altitudes increase is an example of

Accepted Answer

A trend toward the decrease in the size of plants on the slopes of mountains as altitudes increase is an example of a cline, which is a gradual change in a characteristic along a geographic axis.

Question 15

Hardy-Weinberg equilibrium must occur in populations wherein

Accepted Answer

The Hardy-Weinberg equilibrium assumes several conditions including no natural selection (C), but it does not require an allele to remain fixed (A) or for there to be no genetic variation (B). Genetic variation is actually expected under Hardy-Weinberg equilibrium provided the other conditions are met.

Question 16

In modern terminology, diversity is understood to be a result of genetic variation. Which of the following is a recognized source of variation for evolution?

Accepted Answer

Recombination through crossing over during meiosis is a recognized source of genetic variation that can lead to diversity. This process generates new combinations of alleles, which can result in different traits in offspring. Choices A, B, and C are not sources of genetic variation but rather describe errors or changes that can occur within genes or the genetic code itself. Choice D refers to the reproduction of prokaryotic cells, which is not relevant to genetic variation in the context of this question.

Question 17

How many of these statements regarding populations are true?
1)Mature males and females of a population can interbreed with each other.
2)Populations are sometimes geographically isolated from other populations.
3)Biological species are made up of populations.
4)Members of a population tend to be genetically more similar to each other than to members of other populations.
5)Populations have genomes, but not gene pools.

Accepted Answer

1) True, as mature males and females of a population can indeed interbreed, which is a defining characteristic of a population within a species. 2) True, populations can be geographically isolated, leading to variations and potentially speciation over time. 3) True, biological species are indeed composed of various populations that interbreed or have the potential to interbreed. 4) True, members of the same population are generally more genetically similar to each other than to members of other populations due to shared gene flow and breeding practices. 5) False, populations do not have genomes; individuals have genomes. Populations have gene pools, which represent the sum of all genetic information in the population.

Question 18

In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of the allele a is 0.3. What is the percentage of the population that is homozygous for this allele?

Accepted Answer

The frequency of allele a is 0.3, so the frequency of homozygous aa individuals is (0.3)^2 = 0.09, which is 9.0% of the population.

Question 19

Which of these variables is likely to undergo the largest change in value as the result of a mutation that introduces a brand-new allele into a population's gene pool at a locus that had formerly been fixed?

Accepted Answer

Average heterozygosity measures the average proportion of heterozygotes in a population. Introducing a new allele into a previously fixed locus directly increases heterozygosity, as individuals can now be heterozygous at that locus.

Question 20

In the formula for determining a population's genotype frequencies, the 2 in the term 2pq is necessary because

Accepted Answer

The 2 in the term 2pq is necessary because heterozygotes can come about in two ways - one allele from the mother and one from the father. This means there are two possible ways for an individual to be heterozygous, hence the 2 in the formula. The other options (population being diploid, doubling in number, or heterozygotes having two alleles) are true, but do not directly explain the 2 in the formula.

Quiz 23: The Evolution of Populations