BILD 3 Exam 1 Practice

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).

It is 3AM. You are awakened by a phone call. The mysterious voice asks: "What are the necessary conditions for natural selection to occur within a population?"

1. Variation in a trait in the population 2. The trait is heritable, at least to some extent 3. Differential Reproductive success based on that trait

Which of the following isolating mechanisms are prezygotic and which are postzygotic? (Circle either PRE or POST) 1. Land iguana eggs can't be fertilized by marine iguana sperm. 2. Mules-horse-donkey hybrids-are sterile. 3. In a forest, one beetle species lives on oaks and another beetle species lives on pines. 4. In closely related bird species, males sing different courtship songs.

1.Pre 2.Post 3.Pre 4.Pre

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?

16%

Which of the following would best be described as a case of speciation in sympatry?

An individual hermaphroditic plant undergoes meiotic failure, producing diploid pollen and ovules; these self-fertilize, germinate, and grow into several fully fertile tetraploid plants.

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 correct?

Animals and plants have a common ancestor. Fungi and animals do have a common ancestor. Animals and fungi are more closely related to each other than animals are to land plants.

Which of the following statements explains why animals are less likely than plants to speciate by polyploidy?

Animals rarely self-fertilize, so diploid gametes are much less likely to fuse.

What is the difference between allopatric and parapatric speciation? Why is the latter rare?

Both are a result of reproductive isolation. In allopatric speciation, populations are separated by geographical barriers and reproductive isolation is easy to maintain due to the physical separation of the populations. The geographic barriers prevent gene flow and the forces of evolution act independently on each population, leading to speciation. In parapatric speciation, there is no physical barrier separating two populations which occur side-by-side (thus "para"). Without a physical barrier to gene flow it is difficult to prevent gene flow and maintain reproductive isolation making parapatric speciation rare. It usually occurs because the two adjacent habitats have such different selective pressures that intermediate forms (the product of inter-breeding between the two populations) are selected against (at a severe disadvantage).

Which of these describe one way in which the fossil record is biased?

Certain habitats are more likely to produce fossils than others Recent fossils are more likely to be found than older ones Organisms that lived above ground are more likely to be found than underground Abundant species are more likely to appear in the fossil record than rare species

Which statement best represents the meaning of the term evolution:

Changes in gene frequencies in a population over time

Which of these is true about the Central Dogma of Molecular Biology?

DNA codes for RNA, which codes for Protein It is a one-way flow of information DNA sequences define the genotype, which then produce the proteins that create the phenotype

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 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.

Woese used SSU RNA to build the 3-Domain Tree of Life. When choosing to study that molecule, which of the following was characteristics of RNA that made it a good molecule to use for such a study:

It is a necessary part of the cellular machinery for reproduction and other purposes. It is found in every species. It is passed on through evolutionary history with only minor modifications.

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 variation in traits, heritability of those traits, and differential reproductive success based on those traits - the definition of natural selection.

These graphs show percentage change in three different molecular sequences plotted against time. Which of these would make a good candidate for a molecular clock?

Straight-lined graphs

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.

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?

The frequency of nonresistant forms will increase in these populations.

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?

The percentage of pink flowers should increase over time.

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?

There was enough heritable variation in the wild canine species to create a variety of features.

Applying the principle of parsimony to the trait "ability to fly," which of the two phylogenetic trees above is better?

Tree where only one line points in the other direction compared to the rest

Give a 3-word definition of Natural Selection

Variable, heritable, fitness

Darwin's primary contribution to biological theory was the idea that

an important mechanism of biological evolution is natural selection

Which of the following tend to promote speciation?

founder effect reproductive isolation natural selection

The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in gene frequencies, at many loci, from all other populations including their original homeland. Which of the following likely explains the genetic uniqueness of this population? A) sexual selection and inbreeding depression

founder effect and genetic drift

The HOX genes in fruit flies, annelid worms, clams, and humans show a high degree of sequence similarity. This is an example of:

genetic homology

The two key factors responsible for speciation among populations are:

reproductive isolation and genetic divergence