Practice Test Multiple Choice
What is stabilizing selection and how does it differ from disruptive selection and directional selection? You should include in your answer some explanation of how the mean value for a trait changes in a population under each type of selective pressure.
1.Stabilizing selection selects for the existing mean value of the trait and against extreme values of the trait. Thus, the mean value does not change over time. 2. Disruptive selection selects for both extremes simultaneously and against the mean. Thus, the mean value does not change over time, though the number of individuals with the mean value decreases. The distribution loses its normal distribution (bell shaped curve). Eventually, two means may emerge that lead to divergence and, perhaps, speciation. 3. Directional selection selects for one extreme only. Thus, the mean value of the trait is pushed toward that extreme (either increasing the mean, or decreasing the mean).
Darwin's primary contribution to biological theory was the idea that: A) an important mechanism of biological evolution is natural selection B) new alleles arise through mutation C) evolution is the change in gene frequencies over time D) genes are the units of inheritance E) characteristics acquired during an individual's lifetime can be passed to its offspring
A
On the tree of life, the branch leading to animals is closer to fungi than it is to the branch leading to land plants. Which of the following statements is incorrect? A) Animals and land plants are more closely related to each other than either is to fungi. B) Animals and plants have a common ancestor. C) Fungi and animals do have a common ancestor. D) Animals and fungi are more closely related to each other than animals are to land plants.
A
The HOX genes in fruit flies, annelid worms, clams, and humans show a high degree of sequence similarity. This is an example of: A) genetic homology B) developmental homology C) structural homology D) analogy/convergent evolution
A
Starting from a single wild canine species, humans have developed hundreds of breeds of domestic dogs. Which of the following statements is supported by this observation? A) Natural selection had not occurred very frequently in the wild dog populations. B) There was enough heritable variation in the wild canine species to create a variety of features. C) Heritable variation is low; otherwise the there would be more wild dog species. D) Most of the variation in domestic dog species is a result of variation in nutrition and training.
B
The two key factors responsible for speciation among populations are: A) mutation and heterozygote disadvantage B) reproductive isolation and genetic divergence C) postzygotic isolation and morphological change D) mutation and genetic drift
B
Which of these is NOT true about the Central Dogma of Molecular Biology? A) DNA codes for RNA, which codes for Protein B) It is a two-way flow of information C) It is a one-way flow of information D) DNA sequences define the genotype, which then produce the proteins that create the phenotype
B
Which statement best represents the meaning of the term evolution: A) Changes in species toward greater complexity over time B) Changes in gene frequencies in a population over time C) The strongest individuals survive and produce the most offspring D) Changes in an individual over time in response to natural selection
B
Claytonia virginica is a woodland spring herb with flowers that vary from white to pale pink to bright pink. Slugs prefer to eat pink-flowering over white-flowering plants (due to chemical differences between the two), and plants experiencing severe herbivory were more likely to die. The bees that pollinate this plant prefer also prefer pink to white flowers, so that Claytonia with pink flowers have greater relative fruit set (reproductive success) than Claytonia with white flowers. A researcher observes that the percentage of different flower colors remains stable in the study population from year to year. If the researcher removes all slugs from the study population, what would you expect to happen to the distribution of flower colors in the population over time? A) The distribution of flower colors should not change. B) The percentage of white flowers should increase over time. C) The percentage of pink flowers should increase over time. D) The distribution of flower colors should randomly fluctuate over time.
C
The ability to taste phenylthiocarbamide (PTC) is a trait controlled by 2 alleles (PTC taster and PTC non-taster). Suppose 36% of a remote mountain village cannot taste PTC and must, therefore, be homozygous recessive (aa) for the PTC non-taster allele. If this population conforms to Hardy-Weinberg expectations for this gene, what percentage of the population must be homozygous (AA) for the PTC taster allele? A) 48% B) 40% C) 16% D) 32% E) 60%
C
Which of the following statements explains why animals are less likely than plants to speciate by polyploidy? A) Animals have behavioral rituals that result in mate recognition. B) Animal movement patterns insure gene flow. C) Animals rarely self-fertilize, so diploid gametes are much less likely to fuse. D) Animals chromosomes are less likely to replicate incorrectly than plants.
C
Woese used SSU RNA to build the 3-Domain Tree of Life. When choosing to study that molecule, which of the following was NOT one of the characteristics of RNA that made it a good molecule to use for such a study: A) It is a necessary part of the cellular machinery for reproduction and other purposes. B) It is found in every species. C) It mutates more frequently than expected by chance. D) It is passed on through evolutionary history with only minor modifications.
C
Over the past several decades, natural selection has caused populations of Staphylococcus aureus (an infectious wound bacterium) to evolve resistance to most antibiotics. If antibiotic use were stopped, what would you predict would happen to these S. aureus populations? A) They will go extinct without the antibiotic. B) The frequency of resistant forms will increase in these populations. C) The populations will begin colonizing new environments. D) The frequency of nonresistant forms will increase in these populations.
D
Which of the following does NOT tend to promote speciation? A) founder effect B) reproductive isolation C) natural selection D) gene flow
D
Which of the following would best be described as a case of speciation in sympatry? A) A population of lizards is subdivided by a natural barrier and subsequently diverges to form two species that cannot interbreed. B) Speciation cannot take place in sympatry - only in allopatry, where geography poses a barrier to gene flow. C) A new, isolated population of fruit flies is founded by a small group of colonists, which then diverge from the ancestral source population. D) An individual hermaphroditic plant undergoes meiotic failure, producing diploid pollen and ovules; these self-fertilize, germinate, and grow into several fully fertile tetraploid plants.
D
What does it mean when we say "fitness is relative"?
Fitness is defined in terms of reproductive success relative to others in the population. It is calculated as reproductive success in proportion to the most successful form in the population.
What is the Hardy-Weinberg Equation and what are the assumptions of the HW Rule? The Hardy-Weinberg equation is p2, + 2pq + q2 = 1. The HW equation is a null model, in that it predicts GENOTYPE frequencies in a population if no forces of evolution are working on the population and deals with a diploid population, at a single locus with only 2 alleles and 3 genotypes.
For a population to be in Hardy-Weinberg equilibrium, the assumptions are that the population must be very large to counteract the effects of genetic drift and mutation and very large randomly breeding population with random mating (no sexual selection) will ensure sufficient gene flow among a large number of individuals. Essentially, the assumptions are that there is no selection, no mutation, no drift, and gene flow within the population.
What is the difference between homologous traits and analogous traits and use the following structures as examples: a bird's wing, a dog's leg, and a fly's wing.
Homologous traits are similar traits shared by two species for which an ancestral form was present in a common ancestor. Since the species diverged, the differing selective pressures on the two species generally cause the traits to change in different ways. A bird's wing and a dog's leg are homologous traits in that the bone structure for both was present in a common ancestor. The bone structures now are used in somewhat different ways. This is divergent evolution. Both the dog's leg and the bird's wing were derived traits from a common ancestor. Analagous traits are similar traits shared by two species, but no ancestral form was present in a common ancestor. Similar selective pressures resulted in convergent evolution to produce similar morphologies. The bird's wing and the fly's wing are analogous trait. There is not a common ancestor of both the bird and the fly that had a "wing", but both species gained a selective advantage through flying, which explains why both have wings. NOTE: it is wrong to say "Analagous traits are similar traits in species without a common ancestor". All species have a common ancestor. The difference here is whether or not the trait in question was present in a common ancestor.
What does it mean to say "mutation proposes, selection disposes" and what roles do the genotype and phenotype play in the process?
Mutation is the source of all variation. It is the only source of new alleles. It is a random event. It can produce advantageous, neutral, and disadvantageous changes. In essence, it provides options. Natural selection is not random. It is a filtering process that eliminates disadvantageous changes in genes from the gene pool (and increases the frequency of advantageous geneotypes)
Why can sexual selection be considered a subset of natural selection, even though sexual selection often produces exaggerated traits that lower surivorship of individuals with those exaggerated traits?
Sexual selection is selection on traits that increase success in competing for mating opportunities (i.e., mates). Sexual selection is a special case of natural selection, in that the competition between individuals is for mating opportunities, not survival. Thus, traits arise through sexual selection that may be detrimental to survival, but endow the possessor with an advantage in gaining reproductive success - i.e., differential reproductive success based on that trait. It has varation in traits, heritability of those traits, and differential reproductive success based on those traits - the definition of natural selection.
EXTRA CREDIT (2 pts) Give a 3-word definition of Natural Selection
Variable, heritable, fitness
