BIOL 4003 Exam 3

The pattern of X-linked recessive inheritance is revealed by the following observations:

1. Males are much more likely to exhibit the trait. 2. Mothers of affected males often have brothers or fathers who are also affected. 3. Daughters of affected males produce, on average, 50% affected sons.

The three common explanations for dominant disorders are:

1. haploinsufficiency 2. a gain-of-function mutation 3. a dominant-negative mutation.

What percentage of individuals fall more than 2 SDs above the mean?

About 95.4% are within two standard deviations of the mean, which means that 4.6% are outside of this range. Half of them, or 2.3%, fall more than two standard deviations above the mean.

If a cell cannot make any Rb protein, how will this affect the function of E2F?

E2F will be active all of the time, which will lead to uncontrolled cell division.

Is height a discontinuous (discrete) trait, or does it exhibit a continuum?

In most populations height exhibits a continuum.

Is Carbon Copy a transgenic animal?

No. Carbon Copy did not receive any genetic material from a different species.

Are polymorphisms common or rare in natural populations?

Polymorphisms are very common in nearly all natural populations.

The function of photolyase is to repair a. double-strand breaks. b. apurinic sites. c. thymine dimers. d. all of the above.

c. thymine dimers.

The underlying cause(s) of epigenetic changes associated with cancer may be a. mutations in genes that encode chromatin-modifying proteins. b. environmental agents that alter the function of chromatin-modifying proteins. c. mutations in genes that encode proteins that directly accelerate cell growth. d. all of the above. e. both a and b.

e. both a and b.

Five common features of autosomal dominant inheritance:

1. An affected offspring usually has one or two affected parents. However, this is not always the case. Some dominant traits show incomplete penetrance (see Chapter 4), so a heterozygote may not exhibit the trait even though it may be passed to offspring who do exhibit the trait. Also, a mutation that produces the dominant allele may occur during gametogenesis, so two unaffected parents may produce an affected offspring. 2. An affected individual with only one affected parent is expected to produce 50% affected offspring (on average). 3. Two affected, heterozygous individuals have (on average) 25% unaffected offspring. 4. The trait occurs with the same frequency in both sexes. 5. For most dominant, disease-causing alleles, the homozygote is more severely affected with the disorder. In some cases, a dominant allele may be lethal in the homozygous condition.

Four common features of autosomal recessive inheritance:

1. Frequently, an affected offspring has two unaffected parents. For rare recessive traits, the parents are usually unaffected, meaning they do not exhibit the disease. For deleterious alleles that cause early death or infertility, the two parents must be unaffected. This is always the case for TSD. 2. When two unaffected heterozygotes have children, the percentage of affected children is (on average) 25%. 3. Two affected individuals have 100% affected children. This observation can be made only when a recessive trait produces fertile, viable individuals. In the case of TSD, the affected individual dies in early childhood, and so it is not possible to observe crosses between two affected people. 4. The trait occurs with the same frequency in both sexes.

For those X-linked dominant disorders in which the offspring can reproduce, the following pattern is often observed:

1. Only females exhibit the trait when it is lethal to males. 2. Affected mothers have a 50% chance of passing the trait to daughters. Note: Affected mothers also have a 50% chance of passing the trait to sons, but for many of these disorders, affected sons are not observed because of lethality.

What is a checkpoint?

A checkpoint is a point in the cell cycle at which checkpoint proteins determine if the cell is in the proper condition to divide. If an abnormality such as DNA damage is detected, these proteins will halt the cell cycle.

Explain how a DNA microarray provides information regarding the expression of genes.

A key point is that mRNA is made only when a gene is expressed. In this experiment, mRNA is first isolated and then used to make cDNA, which is fluorescently labeled. The fluorescent spots indicate which genes have been transcribed to produce mRNA.

Explain why familial breast cancer shows a dominant pattern of inheritance in a pedigree even though it is recessive at the cellular level.

An individual with a predisposition for developing familial breast cancer inherits only one copy of the mutant allele. Therefore, the disease shows a dominant pattern of inheritance. However, for the individual to actually get breast cancer, the other allele must become mutant in somatic cells.

What is happening at the bottleneck? Describe the effect of genetic drift following the bottleneck.

At the bottleneck, genetic diversity may be reduced because there are fewer individuals in the population. During the bottleneck, genetic drift may promote the loss of certain alleles and the fixation of other alleles, thereby lowering the genetic variation even more.

How does population size affect genetic drift?

Genetic drift tends to have a greater effect in small populations. It can lead to the rapid loss or fixation of an allele.

Are hematopoietic stem cells unipotent, multipotent, or pluripotent?

Hematopoietic stem cells are multipotent.

What is the difference between a gene knockout and a gene knockin?

In a gene knockout, the function of a gene is eliminated. For diploid organisms, both copies are inactivated. In a gene knockin (in mice), a gene is added to a noncritical site in the genome.

How does inbreeding affect the likelihood that recessive traits will be expressed? Explain.

Inbreeding increases the likelihood of homozygosity, and therefore tends to increase the likelihood that an individual will exhibit a recessive trait. This occurs because an individual can inherit both copies of the same allele from a common ancestor.

Explain how gene number and environmental variation affect the overlaps between phenotypes due to different genotypes.

Increases in gene number and more environmental variation tend to cause greater overlaps between phenotypes due to different genotypes.

In general, why does stabilizing selection decrease genetic diversity?

Stabilizing selection decreases genetic diversity because it eliminates individuals that carry alleles that promote more extreme phenotypes.

In the cloning protocol, why is the nucleus of the oocyte removed?

The nucleus of the oocyte is removed so that the resulting organism contains (nuclear) genetic material only from the somatic cell.

When we say that alleles are additive, what does it mean?

When alleles are additive, they contribute in an incremental way to the outcome of a trait. Having three red alleles, for example, will make the hull color of a wheat plant darker red than it will be with two red alleles.

Explain why stem cells are not depleted during the life of an organism.

When stem cells divide, they produce one cell that remains a stem cell and another cell that differentiates. This pattern maintains a population of stem cells.

Explain how negative frequency-dependent selection works.

With negative frequency-dependent selection, the rarer phenotype has a higher fitness, which improves its reproductive success.

Does disruptive selection favor polymorphism? Explain why or why not.

Yes, disruptive selection fosters polymorphism. The fitness values of the resulting phenotypes depend on the environment. Some phenotypes are the fittest in one environment, whereas other phenotypes are the fittest in another environment.

A gene exists in two alleles designated D and d. If 48 copies of this gene are the D allele and 152 are the d allele, what is the allele frequency of D? a. 0.24 b. 0.32 c. 0.38 d. 0.76

a. 0.24

Which of the following is a factor that, by itself, does NOT promote widespread changes in allele or genotype frequencies? a. New mutation b. Natural selection c. Genetic drift d. Migration e. Nonrandom mating

a. New mutation

A collection of recombinant vectors that carry fragments of chromosomal DNA is called a. a genomic library. b. a cDNA library. c. a Northern blot. d. either a or b.

a. a genomic library.

A mutation in one gene that reverses the phenotypic effects of a mutation in a different gene is a. an intergenic suppressor. b. an intragenic suppressor. c. an up promoter mutation. d. a position effect.

a. an intergenic suppressor.

In nucleotide excision repair in E. coli, the function of the UvrA/UvrB complex is to a. detect DNA damage. b. make cuts on both sides of the damage. c. remove the damaged piece of DNA. d. replace the damaged DNA with undamaged DNA.

a. detect DNA damage.

Within a particular population, darkly colored rats are more likely to survive than more lightly colored individuals. This situation is likely to result in a. directional selection. b. stabilizing selection. c. disruptive selection. d. balancing selection.

a. directional selection.

When a cloned gene is inserted into a noncritical site in the mouse genome by homologous recombination, the result is a. gene addition. b. gene modification. c. gene knockout. d. both a and b.

a. gene addition.

In natural populations, most genes are a. polymorphic. b. monomorphic. c. recessive. d. both a and c.

a. polymorphic.

The identification of a stop codon for a particular gene is an example of a. sequence recognition. b. pattern recognition. c. both a and b. d. none of the above.

a. sequence recognition.

In an Ames test, a ____________ number of colonies is observed if a substance ________ a mutagen, compared with the number of colonies for a control sample that is not exposed to the suspected mutagen. a. significantly higher, is b. significantly higher, is not c. significantly lower, is d. significantly lower, is not

a. significantly higher, is

Homologous recombination refers to the exchange of DNA segments that are a. similar or identical in their DNA sequences. b. in close proximity to one another. c. broken due to ionizing radiation. d. misaligned along a chromosome.

a. similar or identical in their DNA sequences.

A key difference between the original Holliday model and the double-strand break model is the way that a. the DNA strands are initially broken. b. branch migration occurs. c. a heteroduplex is formed. d. resolution occurs.

a. the DNA strands are initially broken.

The function of reverse transcriptase is to a. use RNA as a template to make DNA. b. use DNA as a template to make RNA. c. translate RNA into protein. d. translate DNA into protein.

a. use RNA as a template to make DNA.

A gene knockout is a gene a. whose function has been inactivated. b. that has been transferred to a different species. c. that has been moved to a new location in the genome. d. that has been eliminated from a species during evolution.

a. whose function has been inactivated.

A mutagen that is a base analog is a. ethyl methanesulfonate (EMS). b. 5-bromouracil. c. UV light. d. proflavin.

b. 5-bromouracil.

Which of the following is not a common explanation for a dominant disorder? a. Haploinsufficiency b. A change in chromosome number c. A gain-of-function mutation d. A dominant-negative mutation

b. A change in chromosome number

Which of the following statistics is used to compare two variables? a. Mean b. Correlation coefficient c. Variance d. Standard deviation

b. Correlation coefficient

Which of the following methods is used to detect a specific RNA within a mixture of many different RNAs? a. Site-directed mutagenesis b. Northern blotting c. Western blotting d. None of the above

b. Northern blotting

Which of the following methods use(s) a labeled nucleic acid probe, such as a labeled fragment of DNA? a. Site-directed mutagenesis b. Northern blotting c. Western blotting d. Both a and b

b. Northern blotting

Which of the following would NOT be consistent with the idea that a disorder has a genetic component? a. The disorder is more likely to occur among an affected person's relatives than in the general population. b. The disorder can spread to individuals sharing similar environments. c. The disorder tends to develop at a characteristic age. d. A correlation is observed between the disorder and a mutant gene.

b. The disorder can spread to individuals sharing similar environments.

Which of the following influences on genetic drift involve(s) the migration of a population from one location to another? a. The bottleneck effect b. The founder effect c. Both a and b d. None of the above

b. The founder effect

What is the key reason why the A and B chains of insulin are made as fusion proteins with β-galactosidase? a. To make purification easier b. To prevent their degradation c. To be secreted from the cell d. All of the above are reasons for making the chains as fusion proteins.

b. To prevent their degradation

A mutant gene that promotes cancer when it is overexpressed is called a. a tumor-suppressor gene. b. an oncogene. c. both a and b. d. neither a nor b.

b. an oncogene.

The restriction enzymes used in gene-cloning experiments ___________, which generates sticky ends that can ___________. a. cut the DNA, enter bacterial cells b. cut the DNA, hydrogen bond with complementary sticky ends c. methylate DNA, enter bacterial cells d. methylate DNA, hydrogen bond with complementary sticky ends

b. cut the DNA, hydrogen bond with complementary sticky ends

Nitrous acid replaces amino groups with keto groups, a process called a. alkylation. b. deamination. c. depurination. d. crosslinking.

b. deamination.

Locus heterogeneity means that a genetic disorder a. has a heterogeneous phenotype. b. is caused by mutations in two or more different genes. c. involves a structural change in multiple chromosomes. d. is inherited from both parents.

b. is caused by mutations in two or more different genes.

In reverse transcriptase PCR, the starting biological material is a. chromosomal DNA. b. mRNA. c. proteins. d. all of the above.

b. mRNA.

A mutation changes a codon that specifies tyrosine into a stop codon. This type of mutation is a a. missense mutation. b. nonsense mutation. c. frameshift mutation. d. neutral mutation.

b. nonsense mutation.

An advantage of translesion-replicating polymerases is that they can replicate _________________, but a disadvantage is that they _________________. a. very quickly, have low fidelity b. over damaged DNA, have low fidelity c. when resources are limited, are very slow d. over damaged DNA, are very slow

b. over damaged DNA, have low fidelity

Darwinian fitness is a measure of a. survival. b. reproductive success. c. heterozygosity of the gene pool. d. polymorphisms in a population.

b. reproductive success.

In the replica-plating experiments of the Lederbergs, bacterial colonies appeared at the same locations on each of two secondary plates because a. T1 phage caused the mutations to happen. b. the mutations occurred on the master plate prior to T1 exposure and prior to replica plating. c. Both a and b are true. d. Neither a nor b is true.

b. the mutations occurred on the master plate prior to T1 exposure and prior to replica plating.

During Western blotting, the primary antibody recognizes a. the secondary antibody. b. the protein of interest. c. an mRNA of interest. d. a specific fragment of chromosomal DNA.

b. the protein of interest.

The purpose of a ChIP-chip assay is to determine a. the expression levels of particular genes in a genome. b. the sites in a genome where a particular protein binds. c. the amount of a specific protein that is made in a given cell type. d. any of the above.

b. the sites in a genome where a particular protein binds.

When a dideoxyribonucleotide is incorporated into a growing DNA strand, a. the strand elongates faster. b. the strand cannot elongate. c. the strand becomes more susceptible to DNase I cleavage. d. none of the above events occurs.

b. the strand cannot elongate.

One strategy for producing a protein in the milk of a cow is to place the coding sequence of the gene of interest next to a __________ and then inject the gene into a _________. a. lac operon promoter, cow oocyte b. β-lactoglobulin promoter, cow oocyte c. lac operon promoter, cow mammary cell d. β-lactoglobulin promoter, cow mammary cell

b. β-lactoglobulin promoter, cow oocyte

Which of the following is not an example of a spontaneous mutation? a. A mutation caused by an error in DNA replication b. A mutation caused by a tautomeric shift c. A mutation caused by UV light d. All of the above are spontaneous mutations.

c. A mutation caused by UV light

Which of the following was the first living organism to be patented? a. A strain of E. coli that makes somatostatin b. A strain of E. coli that makes insulin c. An oil-eating bacterium d. A strain of B. thuringiensis that makes an insecticide

c. An oil-eating bacterium

For the method of RNA sequencing (RNA-Seq), which of the following is the correct order of steps? a. Isolate RNAs, synthesize cDNAs, fragment RNAs, sequence cDNAs, align cDNA sequences b. Synthesize cDNAs, sequence cDNAs, isolate RNAs, fragment RNAs, align cDNA sequences c. Isolate RNAs, fragment RNAs, synthesize cDNAs, sequence cDNAs, align cDNA sequences d. Synthesize cDNAs, isolate RNAs, fragment RNAs, sequence cDNAs, align cDNA sequences

c. Isolate RNAs, fragment RNAs, synthesize cDNAs, sequence cDNAs, align cDNA sequences

One way that TNRE may occur involves the formation of _________ that disrupts ____________. a. a double-strand break, chromosome segregation b. an apurinic site, DNA replication c. a hairpin, DNA replication d. a free radical, DNA structure

c. a hairpin, DNA replication

During mammalian reproductive cloning, _________ is fused with __________. a. a somatic cell, a stem cell b. a somatic cell, an egg cell c. a somatic cell, an enucleated egg cell d. an enucleated somatic cell, an egg cell

c. a somatic cell, an enucleated egg cell

A gene pool is a. all of the alleles of the genes in a single individual. b. all of the genes in the gametes produced by a single individual. c. all of the alleles of all the genes in a population of individuals. d. the random mixing of alleles during sexual reproduction.

c. all of the alleles of all the genes in a population of individuals.

The purpose of site-directed mutagenesis and CRISPR-Cas technology is to a. determine if a protein binds to a DNA segment. b. determine the sequence of a segment of DNA. c. alter the sequence of a segment of DNA. d. determine if a gene is expressed.

c. alter the sequence of a segment of DNA.

In one PCR cycle, the correct order of steps is a. primer annealing, primer extension, denaturation. b. primer annealing, denaturation, primer extension. c. denaturation, primer annealing, primer extension. d. denaturation, primer extension, primer annealing.

c. denaturation, primer annealing, primer extension.

A population occupies heterogeneous environments in which the fitness of some genotypes is higher in one environment and the fitness of other individuals is higher in another environment. This situation is likely to result in a. directional selection. b. stabilizing selection. c. disruptive selection. d. balancing selection.

c. disruptive selection.

Homologous genes a. are derived from the same ancestral gene. b. are likely to carry out the same or similar functions. c. have similar DNA sequences. d. exhibit all of the above features.

c. have similar DNA sequences.

The BLAST program begins with a particular genetic sequence and a. translates it into an amino acid sequence. b. determines if it contains one or more genes. c. identifies homologs within a database. d. does all of the above.

c. identifies homologs within a database.

A DNA microarray is a slide that is dotted with a. mRNAs from a sample of cells. b. fluorescently labeled cDNAs. c. known sequences of DNA. d. known cellular proteins.

c. known sequences of DNA.

A down promoter mutation causes the promoter of a gene to be _______ like the consensus sequence and _________ transcription. a. less, stimulates b. more, stimulates c. less, inhibits d. more, inhibits

c. less, inhibits

Inbreeding is sexual reproduction between individuals that are a. homozygous. b. heterozygous. c. part of the same genetic lineage. d. both a and c.

c. part of the same genetic lineage.

Saying that a quantitative trait exhibits a continuum means that a. the numerical value for the trait increases with the age of the individual. b. environmental effects are additive. c. the phenotypes for the trait are continuous and do not fall into discrete categories. d. the trait continuously changes during the life of an individual.

c. the phenotypes for the trait are continuous and do not fall into discrete categories.

Tumor-suppressor genes promote cancer when a. they are overexpressed. b. they are expressed in the wrong cell type. c. their function is inactivated. d. they are expressed at the wrong stage of development.

c. their function is inactivated.

The allele frequency of C is 0.4 and that of c is 0.6. If the population is in Hardy-Weinberg equilibrium, what is the frequency of heterozygotes? a. 0.16 b. 0.24 c. 0.26 d. 0.48

d. 0.48

Which of the following DNA repair systems may involve the removal of a segment of a DNA strand? a. Base excision repair b. Nucleotide excision repair c. Mismatch repair d. All of the above

d. All of the above

Which of the following uses of microorganisms is/are important to humans? a. Production of medicines b. Food fermentation c. Biological control d. All of the above are important to humans.

d. All of the above are important to humans.

Which of the following is an example of a quantitative trait? a. Height b. Rate of glucose metabolism c. Ability to learn a maze d. All of the above are quantitative traits.

d. All of the above are quantitative traits.

Which of the following is a type of genetic change that could produce an oncogene? a. Missense mutation b. Gene amplification c. Chromosomal translocation d. All of the above can produce an oncogene.

d. All of the above can produce an oncogene.

Which of the following types of epigenetic changes may promote cancer? a. DNA methylation b. Covalent modification of histones c. Chromatin remodeling d. All of the above may promote cancer.

d. All of the above may promote cancer.

The variance is a. a measure of the variation around the mean. b. computed as a squared deviation. c. higher when there is less phenotypic variation. d. Both a and b are correct.

d. Both a and b are correct.

Which of the following is a key feature of stem cells? a. They have the ability to divide. b. They have the ability to differentiate. c. They are always pluripotent. d. Both a and b are true of stem cells.

d. Both a and b are true of stem cells.

Which of the following mechanisms can result in gene conversion? a. DNA mismatch repair b. DNA gap repair c. Resolution of a Holliday junction d. Both a and b can result in gene conversion.

d. Both a and b can result in gene conversion.

Which of the following is an example of a somatic mutation? a. A mutation in an embryonic muscle cell b. A mutation in a sperm cell c. A mutation in an adult nerve cell d. Both a and c are examples of somatic mutations.

d. Both a and c are examples of somatic mutations.

Which of the following may be used as a vector in a gene-cloning experiment? a. mRNA b. Plasmid c. Virus d. Either b or c

d. Either b or c

During the molecular process of homologous recombination between homologous chromosomes, a. a Holliday junction forms. b. branch migration occurs. c. a heteroduplex region forms. d. all of the above occur.

d. all of the above occur.

Genetic drift is a. a change in allele frequencies due to random fluctuations. b. likely to result in allele loss or fixation over the long run. c. more pronounced in smaller populations. d. all of the above.

d. all of the above.

A point mutation could be caused by a. depurination. b. deamination. c. tautomeric shift. d. any of the above.

d. any of the above.

Normal (nonmutant) tumor-suppressor genes often function a. as negative regulators of cell division. b. in the maintenance of genome integrity. c. in the stimulation of cell division. d. as both a and b.

d. as both a and b.

A gene exists in two alleles, and the heterozygote has the highest fitness. This situation is likely to result in a. directional selection. b. stabilizing selection. c. disruptive selection. d. balancing selection.

d. balancing selection.

Gene flow depends on a. migration. b. the ability of migrant alleles to be passed to subsequent generations. c. genetic drift. d. both a and b.

d. both a and b.

During real-time PCR, the synthesis of PCR products is analyzed a. at the very end of the reaction by gel electrophoresis. b. at the very end of the reaction by fluorescence that is emitted within the thermocycler. c. during the PCR cycles by gel electrophoresis. d. during the PCR cycles by fluorescence that is emitted within the thermocycler.

d. during the PCR cycles by fluorescence that is emitted within the thermocycler.

Double-strand breaks can be repaired by a. homologous recombination repair (HRR). b. nonhomologous end joining (NHEJ). c. nucleotide excision repair (NER). d. either a or b.

d. either a or b.

Personalized medicine may be used a. to characterize types of tumors. b. to predict the outcome of certain types of cancers. c. to determine the proper dosage of drugs. d. in all of the above.

d. in all of the above.

Most forms of cancer involve a. the activation of a single oncogene. b. the inactivation of a single tumor-suppressor gene. c. the activation of multiple oncogenes. d. the activation of multiple oncogenes and the inactivation of multiple tumor-suppressor genes.

d. the activation of multiple oncogenes and the inactivation of multiple tumor-suppressor genes.

Which is the proper order of the following steps in a gene-cloning experiment involving vectors? 1. Add DNA ligase. 2. Incubate the chromosomal DNA and the vector DNA with a restriction enzyme. 3. Introduce the DNA into living cells. 4. Mix the digested chromosomal DNA and vector DNA together. e. 1, 2, 3, 4 f. 2, 3, 1, 4 g. 2, 4, 1, 3 h. 1, 2, 4, 3

g. 2, 4, 1, 3