Evolutionary Biology Exam 2 Practice Questions

Explain the difference between coding and noncoding segments of DNA.

- Coding segments of DNA are called exons. It contains the information that will be used to encode a protein from the mRNA strand. - Noncoding segments of DNA are called introns. They are removed from the mRNA by RNA splicing. The noncoding portion includes regulatory elements, pseudogenes, and genes encoding functional RNA molecules.

Explain why independent assortment and genetic recombination are important to evolution.

- Genetic recombination occurs randomly in meiosis during the crossing over of paired chromosomes resulting in the chromosomes differing from their parental chromosomes by the time they are packaged into gamete cells. It forms new combos of alleles and is an important source of heritable variation. - Independent assortment occurs during the final stage of meiosis when each pair of chromosomes separates so that only a single copy is in each daughter cell. Which copy ends up in what cell occurs randomly. So, this means a single sperm cell may inherit the maternal copy of one chromosome and the paternal copy of another. This random mixing of maternal and paternal copies results in the production of genetically unique gametes.

Describe 3 mechanisms that influence gene expression.

- Repressors, enhancers, and transcription factors. - Epigenetic modifications like DNA coiling and DNA methylation. - Hormones: signals that flow from cells in one part of the body to cells in another part and act directly or indirectly to alter expression of target genes. - MicroRNA: post-transcriptional regulators that can enhance or silence. Ex: if they bind to mRNA molecules they can silence genes. - RNA splicing: can influence how much of the RNA is available for translation. -Alternative splicing: combining different subsets of exons together, creating different mRNA transcripts from a single gene.

Evaluate the evidence for the role of humans as selective agents in the evolution of plants and animals.

- Reverse of selection in stickleback fish by cleaning pollution in Lake Washington. Therefore, the trout can see the stickleback fish more clearly and hunt them, so the stickleback have reverted back to being more heavily armed to protect themselves from the increase in predation. - Here your more thinking of crops and animals. Like dogs, cattle, maize corn, pesticide resistance, etc.

Discuss the effects of genetic drift on large and small populations.

- Small populations have an increased chance of genetic drift because with a small sample size you increase the probability that the allele frequencies would deviate strongly from the frequencies in the entire population just by chance. Also, the smaller the population the more dramatically allele frequencies fluctuate between generations and the sooner the allele became fixed or lost. In large populations, allele frequencies did not change very much due to drift, and in no case was an allele lost over this time period. Genetic drift eliminates alleles faster in small populations than in bigger ones. (Ex: jelly bean jar)

Differentiate between somatic mutations and germ-line mutations and their roles in variation within a population.

- Somatic mutations are mutations of the body. They affect all the daughter cells produced by the affected cell and can affect the phenotype of the individual. (Ex: if a skin cell is mutated all the cells that come from that skin cell will be mutated, but when we die, the mutation will end. It will not be passed down to our offspring. Not heritable. They cannot be passed down in animals, but can be passed down in plants through vegetative reproduction. - Germ-line mutations are mutations that affect the gametes. They can be transmitted from parent to offspring. Since they're heritable, they create the heritable genetic variation that is important for evolution.

Explain how location and timing of the expression of developmental genes influence limb and beak development.

- The Hoxd13a gene was in charge of creating a fin, but in tetrapods, it has the first wave of that gene, which extends the 'fin', but then there comes a second wave which resulted in an extra appendage at the end and could have led to the formation of tetrapods. So, the fish had the genes for the formation of appendages, but the extra appendages only formed when Hoxd13a was switched on an extra time later in development. - Bmp4 gene and calmodulin affected finches, specifically the concentration of them present affected the finches beak size. A lot of Bmp4 created a deep and wide beak, while little Bmp4 created a narrow beak. A lot of calmodulin resulted in long beaks while low amount of calmodulin resulted in short beaks.

Describe two examples where proteins were co-opted for other functions.

- These are known as promiscuous proteins since they are capable of carrying out more than one function. It allows them to bind to one molecule strongly and another molecule weakly. If the environment of an organism changes so that there is an advantage to binding more tightly to the second target, natural selection may favor mutations that alter the shape of the protein in ways that improve the protein's task. - Another way proteins can have new functions is gene duplication. Once there are two copies of the same gene (paralogs) one copy can continue to perform the gene's original function while the other copy is free to evolve.

Describe the organization of DNA within a human cell.

A molecule of DNA consists of two strings of nucleotides that wind together to form a double helix. In human and eukaryotic cells, DNA is stored in the nucleus and the mitochondria. Nuclear DNA is organized into chromosomes in which the molecule is wound around spool-like proteins called histones. By winding and unwinding DNA around histones, cells can expose or hide genes, which can affect how DNA is transcribed.

Explain why Hox genes are considered part of the "genetic toolkit."

Because Hox genes are inherited by all animals with bilateral body symmetry. A hox gene in a fly could be interchanged for a hox gene in a mouse. That's why they are considered to be from an ancient "genetic toolkit". Hox genes function is to participate in regulatory networks with other patterning genes that demarcate the geography of developing animals, determining the relative locations and sizes of body parts. (Anterior to posterior, ventral to dorsal).

Predict the effect of a bottleneck or founder event on allele diversity.

Bottleneck and founder events both are types of genetic drift and there is a loss of allelic variation. Rare alleles are the most likely to be lost. The amount that the allele diversity decreases depends on the severity of the bottleneck or founder event (how small the population gets in comparison to the original population). Ex of bottleneck: elephant seals. Ex of founder effect: The Bounty at Pitcairn, Norfolk Island.

How does sexual reproduction contribute to the quantity of genetic diversity among individuals of a population?

By separating, combining, and mixing alleles as a result of independent assortment and genetic recombination.

Which of the following is NOT a protein? A) Histone B) Insulin C) Nucleotide D) Hemoglobin E) All of the above are proteins

C) Nucleotide

Who incorporated the idea that the theory of evolution required the capacity for one generation to pass on its traits to the next? A) Charles Darwin B) Jean-Baptiste Lamarck C) Alfred Russel Wallace D) All of the above E) None of the above

D) All of the above. So, Charles Darwin, Jean-Baptiste Lamarck, and Alfred Russel Wallace all required the capacity for one generation to pass on its traits to the next as a part of the theory of evolution.

Which of the following is/are part of the environmental control of gene expression? A) Signals from outside of the body. B) Signals from other genes within the cell. C) Signals from other cells. D) All of the above. E) None of the above.

D) All of the above. So, environmental control of gene expression includes: - Signals from outside the body. - Signals from other genes within the cell. - Signals from other cells.

What is an allele? A) One of several alternative forms of the DNA sequence of the same locus. B) One of several alternative forms of a gene that occur at the same place on paired chromosomes. C) One of several alternative forms of a gene that occur at the same locus in different individuals. D) All of the above. E.) None of the above.

D) All of the above. So an allele consists of the following: - One of several alternative forms of the DNA sequence of the same locus. - One of several alternative forms of a gene that occur at the same place on paired chromosomes. - One of several alternative forms of a gene that occur at the same locus in different individuals.

Compare and contrast the factors leading the directional and stabilizing selection and the outcomes of each.

Directional selection is when you have the trait going towards a certain way because of selecting factors. So for example, the bird beaks when there was a drought, there was a directional selection towards larger beaks so they could crack open the big seeds since the small grass seeds weren't available. Stabilizing selection is when agents of selection act in opposition, the net effect can be a balance, and it selects for an intermediate trait value. For example, like the flies' galls. They needed to be an intermediate size because if they were too big the birds would detect them and scoop the larvae out. If they were too small the parasitoid wasps would drill into the center and lay her eggs there and the wasp larvae would eat the fly larvae and the plant.

How would you describe the development of horns in dung beetles? A) Horn development is a phenotypically plastic trait. B) Horn development is a result of dominant alleles. C) Horn development is polyphenic. D) All of the above. E) A and C only.

E) A and C only. So, horn development in dung beetles is a phenotypically plastic trait and it is polyphenic. Also, male dung beetles do produce horns if their body size is 5mm, but only a few, and their horns are relatively small (since 5mm was the turning point).

What is/are the most important factor/s generating genetic diversity among individuals in a population of eukaryotes? A) Mutation B) Independent assortment C) Genetic recombination D) B and C only E) All of the above are important for generating genetic diversity in eukaryotes.

E) All of the above are important for generating genetic diversity in eukaryotes. So, mutation, independent assortment, and genetic recombination all generate genetic diversity in eukaryotes.

Why don't all phenotypic traits occur as discrete, alternative states like Mendel's peas? A) Because variation in the environment can lead to variation in the phenotypes that arise from a single genotype. B) Because the variation in some traits can be attributed to the cumulative action of many genes. C) Because phenotypes result from complex interaction between many different genes and the environment. D) A and C only. E) All of the above.

E) All of the above. So, not all phenotypic traits occur simply in discrete, alternative states like Mendel's peas because: - the variation in the environment can lead to variation in the phenotypes that arise from a single genotype. - the variation in some traits can be attributed to the cumulative action of many genes. - phenotypes result from complex interaction between many different genes and the environment.

Why is heritable variation among individuals an important factor for natural selection? A) Because variation has to be heritable for a species to survive. B) Because variation has to be heritable for individuals to pass down their beneficial mutations. C) Because when individuals respond to the environment, they can pass the traits they acquired on to offspring. D) Because natural selection cannot act when all individuals are absolutely identical. E) Both b and d.

E) Both b and d. So, heritable variation among individuals is important for natural selection because: - Variation has to be heritable for individuals to pass down their beneficial mutations. - Natural selection cannot act when all individuals are identical.

Describe how slight differences in fitness can change the frequencies of alleles within a population over time.

Even when alleles are separated by only a small difference in their average excess of fitness, selection can have big long-term effects. That's because populations grow like investments earning interest. Over time, an allele with a slightly higher average excess for fitness can come to dominate a population. Unlike genetic drift, this compounding power of natural selection is more effective in large populations than smaller ones. High relative fitness is not a guarantee that an allele will spread in a small population because drift can be stronger than those of selection in small populations.

Which of the following statements about genetic recombination is FALSE? A) Genetic recombination acts independently of independent assortment. B) Genetic recombination occurs during the production of sperm. C) Genetic recombination is relatively unimportant to the process of natural selection. D) Genetic recombination is one factor that increases variation within populations of organisms. E) During meiosis, chromosomes can cross over and exchange segments of DNA so that chromosomes of gametes are different than the chromosomes of the parents.

FALSE: C) Genetic recombination is relatively unimportant to the process of natural selection.

Demonstrate how predators can act as agents of selection.

Hopi Hoekstra studies black and white mice. The white mice flourished on the coasts along the white sand because they blended better, and the predators were more likely to eat dark mice. But on the inlands and the dark soil, predators were more likely to eat lighter mice, so you find mostly dark mice there. The predators selected for certain traits because the individuals that escaped detection were able to reproduce and pass on their traits.

Explain why the Hardy-Weinberg equilibrium is a "null model" for evolution.

In order to meet the Hardy-Weinberg equilibrium, there must be no genetic drift, selection, migration, or mutation. So, H-W equilibrium is a "null model" for evolution because by studying how populations deviate from the H-W equilibrium (and the conditions), they can learn about the mechanisms of evolution and understand how the allele frequencies do change.

Compare and contrast the events that occur in transcription and translation.

In transcription, the proteins bind to the promoter region and make their way from the upstream end of the gene to the downstream end. As the proteins travel along, RNA polymerase assembles a new string of nucleotides whose sequence matches that of the template DNA strand. The single stranded molecule produced by the RNA polymerase is mRNA. RNA pol continues to build mRNA until it comes to a stop codon. In translation, the mRNA will serve as a template for the construction of a protein. Translation takes place inside a ribosome. A ribosome binds to the mRNA molecule and works its way down the sequence of bases; it grabs 3 bases at a time, and every codon encodes a different amino acid, which can be added to the growing protein. Amino acids float around the cell, bound to tRNA. Each tRNA binds to a particular codon, delivering a particular amino acid to the protein.

Can a mutation that occurs within a cell during mitosis in a diploid cell be passed on to offspring?

Maybe. It depends on whether the cell is part of the germ line or not.

Which of these statements about the link between phenotypes and genotypes is NOT always true? A) The environment often affects how a phenotype will develop. B) A single genotype can produce multiple phenotypes. C) Human height is controlled by more than one gene. D) Diseases are caused by recessive genes. E) All of the above.

Not always true: D) Diseases are caused by recessive genes.

Explain how pleiotropy affects the response to selection acting on alleles.

Pleiotropy is the condition when a mutation in a single gene affects the expression of more than one different phenotypic trait. Therefore it is possible for a mutation to both help and hinder an organism (antagonistic pleiotropy- mutation with beneficial benefits for one trait and bad effects on other traits). So the net effect of an allele on fitness is the sum of its pleiotropic effects on the organism in question. The benefits vs. disadvantages will help the scale tip, and it depends on the organism's environment.

Analyze the influence of drift and inbreeding on the genetics of populations within a landscape.

Population subdivision enhances the effects of genetic drift, eroding genetic variation from within local subpopulations and causing allele frequencies to diverge from place to place. Gene flow can counteract this if present, and can lead to homogenization in areas.

Describe the structure of proteins.

Proteins are chains of building blocks known as amino acids. Each protein folds in on itself to produce a new structure, such as the beta-pleated sheet and alpha-helix. These proteins can then bend further into more complex shapes or join with other proteins into even larger structures. Example: - Primary Structure: amino acid sequence - Secondary Structure: beta-pleated sheet and alpha-helix - Tertiary Structure: one subunit of hemoglobin - Quaternary Structure: complete hemoglobin made up of four subunits.

Discuss the effects of inbreeding on an individual's fitness.

Rare deleterious alleles can become unmasked in homozygotes due to inbreeding because the parents in these populations tend to be closely related and thus are more likely to share rare alleles than are two people picked at random. When these rare, deleterious alleles are combined in homozygotes, they can cause genetic disorders and reduced fitness. It can also cause infertility. As people produce fewer offspring due to decreased fitness, this can cause alleles to be removed from the population and therefore have less genetic variation. This is known as inbreeding depression. It will make harmful mutations more common.

Explain why natural selection cannot drive dominant alleles to fixation within a population.

Rare recessive alleles are almost always carried by heterozygous individuals. Since recessive alleles don't affect the phenotypes of heterozygotes, they remain largely hidden from the action of selection. Drift might increase its frequency and it may be affected by selection if heterozygotes mate and produce homozygotes again, but even if it selects against it, it will only go back to hiding in heterozygote individuals once more. Dominant alleles on the other hand cannot hide from selection. So, selection can drive dominant alleles to high frequency, but it can't drive it to fixation because it cannot eliminate the ancestral recessive allele.

Explain how mutations to a regulatory network may affect development of an organism.

Regulatory networks are big systems of interacting genes, transcription factors, promoters, RNA, etc. They function like biological circuits. Many of the genes are organized in hierarchies so the expression of just a few genes trigger the expression of many genes. Therefore if you have a mutation to a regulatory network, it could have big consequences to many genes even if the mutation is a change in a single gene. For example, Hox genes are important developmental genes in animals that encode transcription factors that determine the identity of the body parts along the head-to-tail body axis. Mutations to the Hox gene network could lead to huge deformations. A leg could grow from a fly's head where you would normally have an antennae, because the Hox gene could assign an incorrect identity to the cells in a region of the fly embryo.

Discuss how scientists use laboratory studies to gain insight to natural selection.

Richard Lenski has an experiment where he monitors 12 E. coli colonies that were derived from the same ancestor. It's been going on for 25 years now. He freezes some of the time periods, but that doesn't kill the bacteria so he can thaw it and compare it to current descendants to compare how fast each one grew as a measure of relative fitness. The relative fitness of all groups has increased by 75%. They all evolved in response to natural selection. They had all accumulated mutations that made them more efficient at growing under the conditions that Lenski set up. The fitness of the bacteria is also on the incline. They can also compare genes like the BoxG1 mutation and it diverts resources from building thick membranes to other functions to speed up reproduction and for these bacteria it raises their fitness.

Explain how selection can act to either remove or maintain allelic diversity.

Selection can reduce genetic diversity by driving some alleles to fixation and eliminating others from populations. But under certain conditions, selection can foster variation. Two examples are negative frequency-dependent selection and heterozygote advantage. With negative frequency-dependent selection, the relative fitness of a genotype is high when its rare, but low when its common. Ex: the purple and white orchids in France. With heterozygote advantage, you need the two different alleles at the locus to get higher fitness. For example, sickle cell anemia if you have SS, but you aren't protected from malaria if you have AA, so if you have SA you don't have sickle cells and are protected from malaria.

Analyze the role of the environment on gene expression.

The environment can produce large variations in the expression of a trait. The environment for a gene inside a cell can be anything that interacts with its promoter region in a way that influences whether the gene is expressed. Some phenotypic traits are relatively unaffected by differences in these signals. Ex: humans are always born with 2 eyes, we don't grow 5 or 10 eyes based on how much food we eat. But other traits, like height are more sensitive to environmental stimuli and this potential for variation is known as phenotypic plasticity.

Discuss the complex relationship between genotypes and phenotypes.

The genetic makeup of an organism is its genotype, while the manifestation of the genotype is the phenotype. The genotype does affect the phenotype in that if there are not the genes there then there is no option for the phenotype to express it. However, even if the organism has the genotype for a trait, it may not express it due to various factors, such as environmental influence. For example, if there are two phenotypes within a population (genetic polymorphism), in the simple case each phenotype results from a different combo of alleles from a single gene. In a complex case the phenotypes can result from interactions between many genes and the environment. Ex: there are winged and no-winged aphids, there aren't any half-winged aphids. Whether or not they have wings are dependent on the environment. This trait is a polyphenism.

Complete dominance occurs when:

The phenotype of a heterozygote is identical to the homozygote.

What is alternative splicing?

The process of splicing different subsets of exons from the same gene to produce different combinations and therefore different proteins.

Define population genetics.

The study of the distribution of alleles within a populations and the mechanisms that can cause allele frequencies to change over time.

What role do histones play in eukaryotes?

They condense the DNA and they control the transcription of genes.

Explain how natural selection can act on an extended phenotype.

Think about the galls produced by the flies. It led to a stabilizing selection which led to an intermediate size.

Explain how selection can vary across a species' range.

Think kingsnake. The kingsnake mimic'ed the coral snake when the two overlap leading to brighter colors, but when the kingsnake is on its own it doesn't mimic and tones down the coloration because warning coloration wont serve it there and it will be more detectable to predators.