Test 2 (CHs 6-9)

Human populations are polymorphic for the gene coding for the myoglobin protein. There are two different alleles of this gene (A1 and A2). In a 2002 study, Takata et al. found that in a small Japanese population, the frequency of the A1 allele was p = 0.755, while that of the A2 allele was q = 0.245. Calculate the genotypic frequencies for A1A1, A1A2, and A2A2 (in the same order) under the Hardy-Weinberg equilibrium. Choose the best answer.

.57, .37, .06

In a population of birds, wing feather pigmentation is determined by a single gene with a codominant pair of alleles (A1 and A2). Suppose genotype A1A1 has a dark brown wing color, genotype A1A2 is light brown, and birds with the genotype A2A2 have a light beige color. In a population of 1,000 birds, 350 have dark wings, 500 have light brown wings, and 150 have light beige wings. What is the A1 allele frequency in this population?

.60

Imagine that in a large coastal population, the frequency of the A allele is 0.7 and the frequency of the a allele is 0.3 at a neutral locus. If a small group of individuals from this population, with frequency of the A allele of 0.9, manage to reach a distant island in a one time colonization event, estimate the probability that A will become fixed on the island..

.9

An endangered animal species has an effective population size of 50. What is the expected loss of heterozygosity in each generation?

1%

If one human protein contains about 400 amino acids, how many nucleotides need to be in the exons of the corresponding gene to properly code for it?

1200

In a population of about 50 walruses with 30 fertile females, only 4 males are mating, due to strong male-male competition. Suppose that you need to provide some data for the conservation efforts and you are asked to calculate the values of the effective population size (Ne). What would be your best estimate?

15

Imagine a population of 100 individuals, with the initial frequencies A1 = 0.7 and A2 = 0.3. If A1 and A2 are selectively neutral what is the probability that the A2 allele will drift to fixation?

30%

The fruit fly (Drosophila melanogaster) has four pairs of chromosomes. How many chromosomes would you find in an unfertilized egg of this species?

4

In selection experiments on quantitative traits, we often measure a value of the response to selection, R. What is R equal to?

h^2 x S

Suppose that in wild roses, the A locus controls pigmentation of the petals. Red roses (allele A) are completely dominant to the pale pink breed (allele a). If such purebred lines were crossed and their heterozygous offspring (F1) were grown in the experimental garden so that such hybrids might be crossed among themselves, which of the following phenotypes might you expect in the F2 generation?

Both red and pale pink roses (ratio 3:1)

Drosophila melanogaster has a relatively short generation time (a couple of weeks) and is an easy species in which to score phenotypic markers for a number of linked loci. Consequently, an experiment was done with two pairs of linked loci—A,a and B,b with a recombination rate (r) of 0.1 and C,c and D,d with r of 0.01—to see how quickly sexual reproduction and random mating would break down linkage disequilibrium (LD). If experiments were run for 25 generations, starting with a maximum LD between the loci of 0.25, which two linked loci would have a faster decay of LD?

Locus A,a and locus B,b

The Hardy-Weinberg equilibrium serves as a null model for studies of allele frequencies and genotype frequencies in populations. This model begins with a number of basic assumptions about the individuals and population under study, as well as the evolutionary processes in operation. Which of the following is not an assumption of this model?

Mating in the population is not random with respect to the locus in question

Which of Mendel's laws contradicts the blending theory of inheritance

Mendel's first law, the law of segregation

n sickle cell anemia a point mutation leads to a replacement of one amino acid in a hemoglobin unit, responsible for transportation of oxygen. This and any other mutation in a gene that causes amino acid replacement in a polypeptide chain is known as a __________ mutation.

Missense

The proportion of phenotypic variance that results from additive genetic variance is called the __________ heritability.

Narrow-sense

In the southern European plains, a species of flowers comes in two distinct colors, purple and light pink. Botanists noticed that when the pink variant takes over the field, bees more often visit the purple ones, and vice versa. Such unusual switch of the pollinator's preference is probably an example of:

Negative frequency dependent selection

In one species of cichlid fish in Lake Tanganyika, two mouth morphs (the "right-handed" or dextral and "left-handed" or sinistral) show an interesting association between morph type and fitness. Regarding the relative frequencies of the two mouth genotypes, the higher the frequency of either type, the lower is its fitness because of the rapid adaptation of their prey. This frequency-dependent selection on the mouth morphs in cichlids is an example of:

Negative frequency-dependent selection

Genetic drift tends to increase the homozygosity of a population, and if it were the only evolutionary process operating, any finite population would eventually become entirely homozygous. In practice, however, populations do not become entirely homozygous. Why not?

New mutation provides a continual supply of new genetic variation

In quantitative genetics theory, the value of a quantitative trait is sometimes given by the equation P = G + E. We could define P as the _________ of the continuous trait that we are studying.

Phenotypic value

Which of the following might be found in a prokaryotic cell?

Plasmids

Which of the following genotypes of the pathogenic E. coli would you expect to find as the most common today in the United Kingdom following the curtailment of the sulfonamide prescriptions, keeping in mind the evidence that sulfonamide resistance did not decrease? (chart)

RC

Which of the following breaks up or removes linkage disequilibrium from a population?

Sexual reproduction

In the 1850s and 1860s, Mendel bred pea plants and examined the way that traits were passed down across generations. His conclusions, although not accepted during his lifetime, established the foundation for the field of genetics. What is the most relevant summary of these conclusions?

The hereditary factors responsible for traits such as seed shape and flower color are inherited as discrete units

Manx cats come from a remote island near Great Britain. They have either a reduced or absent tail and longer hind legs than forelegs. These cats are always Mm heterozygotes at a single autosomal locus, M. MM homozygous genotypes are aborted prenatally. What is the best evolutionary explanation for the Manx cats' prevalence on this island?

The prevalence of the Manx phenotype in this island is a result of the founder effect

Complete the following sentence: When the narrow-sense heritability is calculated using similarities between parents and offspring, it will correspond to:

The slope of linear regression between the average phenotype of the two parents and the phenotype of the offspring.

The following graph shows the distribution of fitness effects (s) of bacteriophage f1 mutations. Note that values greater than zero indicate beneficial mutations, whereas values less than zero indicate deleterious mutations. What is the best conclusion from this study? (chart)

The vast majority of the mutations had a deleterious effect, but some were beneficial

The following figure illustrates correlations by twin type (MZ or DZ) and sex in a study of the influence of genetics on depression. Monozygotic twins (MZ) develop from one fertilized egg, whereas dizygotic (DZ) twins develop from two independent zygotes. Choose the correct statement based on this data. (chart)

There is a higher correlation for depression in monozygotic twins than dizygotic twins, and therefore, depression may have a genetic component

A type of mutation in which one region of a chromosome is moved to another region of a different chromosome is called:

Translocation

A mutation that results in a replacement of a purine with a pyrimidine is known as a __________ mutation.

Transversion

If a DNA sequence of the template strand (in the 3'-5' direction) reads ATG, what would be the corresponding mRNA codon (in the 5'-3' direction)?

UAC

In a mouse population that contains hybrid New Zealand Black (NZB)/New Zealand White (NZW) mice, NZW homozygotes are phenotypically normal, whereas NZB homozygotes exhibit a number of autoimmune defects. The NZB/NZW heterozygotes experience even more severe autoimmune disease, and they are used as a medical model of the human autoimmune disease lupus. This is an example of:

Underdominance and unstable equilibrium

Choose the statement that best describes evolution when selection is acting against a rare dominant or a recessive allele.

When a dominant allele is rare, natural selection will drive its frequency down very fast, whereas when a recessive allele is rare, it practically remains hidden from selection.

Suppose that you study a rare human genetic disease and find that the mutation rate for this disease is (μ = 0.00012), while the selection (s) acting against this allele is 0.7. What would be the estimated equilibrium frequency for the recessive allele in question?

.00050

Suppose you survey a population in Hardy-Weinberg (H-W) linkage equilibrium with two loci C,c and D,d. The estimated frequencies of these alleles are: f(C) = 0.6, f(c) = 0.4, f(D) = 0.8, and f(d) = 0.2. What is the frequency of the chromosome haplotype Cd?

.12

Imagine that in a fishery laboratory experiment, you need to calculate h2 for the length of the caudal fin. If your average population measurement is 25 mm, the selected individuals had fins of 35 mm on the average, and the offspring had fins of 30 mm on average, what is the narrow-sense heritability?

.5

Suppose that you are studying a population of African elephants and wish to learn more about its evolutionary history using the two linked loci (A,a and B,b). You discover that haplotype frequencies in this population are as follows: AB = 0.40, Ab = 0.10, aB = 0.42, and ab = 0.08. What is the frequency of the allele a in this population?

.50

The purple flower of the F1 offspring of Mendel's parental generation crosses indicated that:

Both a and b (The F1 generation is heterozygous and purple is dominant over white)

Galapagos lava lizards inhabit dry rocky areas and are found on numerous islands in this archipelago. M. Jordan and H. Snell (2008) assessed the genetic diversity of 17 populations of lava lizards. They reasoned that in the absence of gene flow between populations, genetic drift should strongly influence the patterns of diversity at 11 microsatellite markers they sequenced. The following figure summarizes their findings. Which of the following is the best interpretation of this graph? (chart)

A and D (There is a correlation between latitude and genetic diversity and The graph indicates that genetic drift has been operating more strongly in the smaller populations)

In a recent study on fitness consequences of antipredatory behavior and coloration pattern in garter snakes (T. ordinoides), the phenotype space was depicted as a three-dimensional graph where the highest points represent combinations of traits associated with the greatest fitness values. For such situations we could use Sewall Wright's metaphor of the:

Adaptive landscape

Which of the following can cause linkage disequilibrium in a population?

All of the above (Migration, genetic drift, and mutation)

In an early study of black spruce trees in the Hudson Bay area, researchers studying nuclear DNA found no reduction of genetic diversity in post-Ice Age populations, and thus no evidence of founder effects. Why did a recent study, using mitochondrial DNA (mtDNA) show different results regarding the founder effects in black spruce?

All of the above (Mitochondrial DNA (mtDNA) is maternally inherited, and thus it is passed on only through seeds, while it is absent from pollen, Seeds cannot disperse as easily and as far as the pollen, which is carried by the wind, and Different populations of the black spruce have similar composition of nuclear DNA, but very different with respect to mtDNA composition)

What is true of the nearly neutral theory of molecular evolution?

All of the above (Most substitutions are either neutral or mildly deleterious, Species with larger populations tend to have shorter generation times, and Population size plays an important role in determine the outcome of drift and selection)

What is an important difference between individual and population genetics thinking?

All of the above (Population-level thinking tends to focus on changes in populations across generations, Individual-level thinking asks questions such as: what offspring are produced, and in what frequencies, from a given pair of parents?, and Individual- and population-level approaches ask different questions)

Which of the following is correct regarding the quantitative genetics study done by Franks et al. (2007) on a Brassica rapa population in the wilderness of southern California?

All of the above (This study has implications for global warming since it may teach us how plants will respond to ongoing changes in temperature and precipitation, The ability of plant species to respond will depend on whether there is a sufficient genetic variation, as well as strong selection, for traits such as reproductive timing, and Franks and his colleagues were able to measure both heritability and response to selection values in this natural population)

Which statement is false regarding neutral loci in populations that have experienced a population bottleneck?

Allele frequencies in a population are almost always very similar before and after the bottlenecks

Genetic hitchhiking is a phenomenon in which:

Alleles that are closely linked to a locus under selection may change frequencies because of the linkage to a selected allele

Suppose that you collected the allele and genotype frequency data from a natural population. If you found that the expected genotype frequencies were considerably different from your observed genotype frequencies, what would be your first conclusion regarding this population?

At least one of the evolutionary processes is operating in the population

In the Luria and Delbrück experiment on E. coli, two alternative hypotheses were tested. The mutation hypothesis and the acquired inherited resistance hypothesis make different predictions about the distribution of resistant mutants that will be observed upon exposure to the phage. Which of the following predictions, if proven, would have supported the acquired hereditary resistance hypothesis?

At the time of exposure to the phage, all bacterial cells will be phage-sensitive. The process of exposure to the phage will induce phage resistance in a small fraction of the bacterial cells

In the late 1950s Dobzhansky and Pavlovsky wanted to see whether drift could play an important role in populations under natural selection. They used populations of Drosophila pseudoobscura with different frequencies of chromosomal inversions as a model. What did they demonstrate?

Because the small founding population lines exhibited much greater variation in inversion frequency from one line to the next than the large ones, they demonstrated that both drift and selection act together in these populations

Which of the following is the difference between a DNA molecule and an RNA molecule?

DNA is a double-stranded molecule whereas RNA is single-stranded molecule

The major genetic effect of inbreeding in a population is to:

Decrease the number of loci at which the average individual is heterozygous

One of the important facts learned from the experiments in molecular genetics was that most amino acids can be encoded by more than one nucleotide triplet. For this reason, we say that the genetic code is:

Degenerate

A deletion of a coding gene will most likely have a ___________ effect on fitness.

Deleterious

For many years in the United Kingdom, people with urinary tract infections have been treated with sulfonamide antibiotics. These antibiotics used to be very effective against the common pathogen of the urinary tract, E. coli, but in the late 1990s increased resistance among the E. coli strains was documented. In the meantime, worrisome side effects of these drugs were documented as well, so doctors curtailed their use. Which of the following statements is true about the evolution of resistance to the sulfonamides in the last decade?

Despite the infrequent use of sulfonamides, there was little reduction in frequency of resistance among the bacteria.

In mice that are homozygous for the dark-color Agouti allele (D), the effects of the Mc1R locus are entirely masked so that, irrespective of the genotype at Mc1R, the mice have fully dark coloration. However, if at least one copy of the light-color Agouti allele (L) is expressed, the different shades of brown Mc1R locus are revealed (with the particular shade depending on the number of copies of L). This is an example of:

Epistatic effects of the 2 genes

An addition or deletion of one or two base pairs in a gene sequence results in a __________ mutation.

Frameshift

Linked genes are:

Genes on the same chromosome