Genetics Exam 4

Which of the following is a correct statement regarding Angelman and Prader-Willi syndromes? A) Individuals with Angelman and Prader-Willi display different phenotypes because they differ in which gene products are missing. B) Angelman syndrome results when a copy of chromosome 15 that carries a deletion is inherited from the father. C) Prader-Willi syndrome results when a copy of chromosome 15 that carries a deletion is inherited from the mother. D) Prader-Willi and Angelman syndromes are caused by abnormal imprinting of genes on chromosome 15.

A. Individuals with Angelman and Prader-Willi display different phenotypes because they differ in which gene products are missing.

Which of the following types of eukaryotic gene regulation takes place at the level of DNA? A) chromatin modification B) alternative splicing C) post-transcriptional regulation D) both A and B

A. chromatin modification

If a mutation in region 2 of the trp operon leader prevents the formation of the 2+3 antiterminator loop, what would be the effect? A) constant attenuation of transcription even when tryptophan levels are low B) transcription only when tryptophan is absent C) transcription only when tryptophan is present D) constitutive transcription of the trp operon

A. constant attenuation of transcription even when tryptophan levels are low

In a large population, which of the following is most likely to lead to fixation of a recessive allele? A) directional selection B) genetic drift C) migration D) inbreeding E) mutation

A. directional selection

Additive alleles... A) each contribute equally to the phenotype. B) contribute negatively to the phenotype. C) do not contribute to the phenotype. D) have uneven contributions to the phenotype.

A. each contribute equally to the phenotype

Enhancers... A) serve as binding sties for activator proteins. B) are always located upstream of the genes they regulate. C) are required for basal level transcription. D) are trans-acting regulatory elements that control the timing and tissue specificity of gene expression.

A. serve as binding sties for activator proteins.

Given the following information, VG = 15, VD = 6, VI = 2, VE = 20, and VGE = 0 what is the narrow-sense heritability of the trait in question? A) 0.35 B) 0.2 C) 0.5 D) 0.43

B. 0.2

A population of long-hair cats has a narrow-sense heritability value for fur length of h2 = 0.15. The aim is to breed cats with longer fur than the population currently exhibits. The current generation of cats has a mean fur length of 4 cm. The selected individuals that are bred for the next generation have a mean fur length of 6 cm. What is the expected average length of cat fur in the next generation? A) 6.0 cm B) 4.3 cm C) 5.0 cm D) 3.7 cm

B. 4.3

A QTL is... A) a specific gene whose role in contributing to a quantitative trait has been fully characterized. B) a chromosomal region containing a gene that influences a quantitative trait. C) a measurement of the phenotypic variation in a quantitative trait. D) a measurement of the genetic variation in a quantitative trait.

B. a chromosomal region containing a gene that influences a quantitative trait.

If individuals of one genotype respond to changes in the environment differently than individuals of another genotype, this demonstrates _______________ for that trait. A) environmental variance B) genotype-by-environment interaction C) narrow-sense heritability D) genetic variance

B. genotype-by-environment interaction

A group of individuals from the same species that can interbreed with one another is called a _____. A) community B) population C) pool D) race

B. population

Which of the following does NOT lead to evolution of a population? A) mutation B) random mating C) genetic drift D) selection E) migration

B. random mating

Individuals of a tree snake species vary from light to dark coloration. There are a greater proportion of snakes with a medium coloration after several generations. This change is most likely due to... A) disruptive selection B) stabilizing selection C) directional selection D) inbreeding

B. stabilizing selection

For a gene under negative repressible control, the presence of a small molecule... A) would prevent the gene's activator from binding to the DNA, thus reducing transcription. B) would cause the gene's repressor to bind to DNA and inhibit transcription. C) would cause the gene's activator to bind to DNA and stimulate transcription. D) would prevent the gene's repressor from binding to the DNA, thus increasing transcription.

B. would cause the gene's repressor to bind to DNA and inhibit transcription.

In a population of mice, there are two alleles of the A locus, A and a. Tests showed that, in this population, there are 173 mice of genotype AA, 423 Aa, and 258 aa. Calculate the frequency of the A allele. A) 0.20 B) 0.55 C) 0.45 D) 0.90

C. 0.45

Three independently segregating genes with two alleles each, A/a, B/b, and C/c determine plant height additively in a population. The homozygote AABBCC is 66 cm tall and the homozygote aabbcc is 30 cm tall. How much does each additive allele contribute to the height of these plants? A) 5 cm B) 12 cm C) 6 cm D) 11 cm

C. 6 cm

Which of the following statements about histones and gene expression is correct? A) Phosphorylation of cytosines in the DNA regions bound by histones generally leads to a decrease in transcription. B) DNA methylation weakens the association of histones with the DNA, increasing transcription. C) Addition of methyl groups to the tails of histone proteins can lead to either activation or repression of transcription depending on which amino acid is modified. D) Acetylation of histone proteins usually results in repression of transcription.

C. Addition of methyl groups to the tails of histone proteins can lead to either activation or repression of transcription depending on which amino acid is modified.

Which of the following is necessary for natural selection to occur? A) The population must be relatively small. B) There must be no difference in fitness between individuals of different genotypes. C) Variations of the trait must exist in the population. D) There must be adequate food to reduce competition among individuals.

C. Variations of the trait must exist in the population.

Quantitative traits... A) show discontinuous variation of phenotypic expression B) are influenced by a single gene C) are scored by measuring or counting D) all of the above

C. are scored by measuring or counting

A study from Sweden showed that individuals born in the early 1900's whose grandfathers experienced a food shortage during adolescence tended to live longer than those whose grandfathers had abundant food. The most likely explanation for this observation involves __________. A) attenuation of essential genes B) post-transcriptional gene regulation C) epigenetics D) somatic mutations

C. epigenetics

Methylation of CpG islands . . . A) commonly occurs in the 3' untranslated regions (3' UTRs) of genes. B) occurs with higher frequency in actively transcribed regions of DNA. C) is associated with long-term inhibition of gene expression. D) is a universal gene regulation mechanism affecting both prokaryotes and eukaryotes.

C. is associated with long-term inhibition of gene expression.

Which of the following increases genetic diversity within populations and decreases diversity between populations? A) genetic drift B) non-random mating C) migration D) mutation

C. migration

Broad-sense heritability for a trait is 0.95. This indicates that... A) phenotypic variation for the trait stems mostly from environmental influences. B) the trait will respond well to artificial selection. C) most of the phenotypic variation seen for the trait is due to genetic differences between individuals. D) narrow sense heritability for the trait is 0.05.

C. most of the phenotypic variation seen for the trait is due to genetic differences between individuals.

Chromatin remodeling complexes... A) help condense chromatin into compact chromosomes prior to cell division. B) covalently modify the N terminal tails of histones, for example by acetylation. C) use energy from ATP to physically change the position of nucleosomes along a stretch of DNA. D) use siRNAs or miRNAs as a guide to identify regions of chromatin to silence.

C. use energy from ATP to physically change the position of nucleosomes along a stretch of DNA.

Suppose that the frequency of a particular recessive condition in a population is 1/400 and that the population is at Hardy-Weinberg equilibrium. What is the frequency of heterozygotes in the population? A) 0.05 B) 0.9025 C) 0.0025 D) 0.095

D. 0.095

How many genes are involved in controlling a quantitative trait if crossing two homozygotes on opposite ends of the phenotypic spectrum and then intercrossing the F1 results in F2 offspring that fall into 9 phenotypic classes? A) 3 B) 9 C) 18 D) 4

D. 4

Operons . . . A) are transcribed to make a polycistronic mRNA that contains multiple protein-coding regions. B) are much more common in prokaryotes than in eukaryotes. C) often contain genes whose products function in the same biochemical pathway. D) All of the above

D. All of the above

In eukaryotic cells, genes that are coordinately activated by a particular stimulus __________. A) are often recognized by the same transcriptional activators. B) may have short regulatory sequences in common in their promoters or enhancers. C) are physically clustered in the same operon. D) both A and B E) all of the above

D. Both A and B

Three major epigenetic regulatory mechanisms include . . . A) DNA methylation, covalent modification of the inner histone core, and RNA-based gene activation. B) DNA acetylation, covalent modification of the inner histone core, and RNA-based gene silencing. C) DNA acetylation, covalent modification of histone tails, and RNA-based gene activation. D) DNA methylation, covalent modification of histone tails, and RNA-based gene silencing

D. DNA methylation, covalent modification of histone tails, and RNA-based gene silencing

Two neighboring Caribbean islands harbor iguana populations. One island (island A) has a total iguana population of 800, while the other (island B) has a population of 250. On island A, the frequency of an allele p is estimated at 0.75, while this same allele is present at a frequency of 0.90 on island B. If 100 iguanas migrate from island A to island B, what effect does this have on the frequency of allele p on island B? A) It would increase to 0.98. B) It would remain at 0.90. C) It would decrease to 0.75. D) It would decrease to 0.86.

D. It would decrease to 0.86.

Which of these scenarios is likely due to positive assortative mating? A) Grasshoppers randomly select mates based on proximity and breed with as many other grasshoppers as possible. B) In a large population, the frequency of AA and aa genotypes in offspring decreases over many generations. C) Tall, slender males from a native indigenous tribe preferentially select the shortest and most muscular wives that do not resemble their own physique. D) Purebred dachshunds have a higher incidence of degenerative disc disease than mixed breed dogs.

D. Purebred dachshunds have a higher incidence of degenerative disc disease than mixed breed dogs.

In the absence of tryptophan, what happens to the genes within the trp operon? A) Lack of tryptophan increases the level of cAMP, which leads to activation of CAP protein and gene expression. B) The repressor, when not bound by tryptophan, prevents the operon genes from being transcribed. C) The activator binds to the operator and transcription of structural genes takes place. D) The repressor cannot bind to the operator in the absence of tryptophan, so the structural genes get transcribed.

D. The repressor cannot bind to the operator in the absence of tryptophan, so the structural genes get transcribed.

Is the following statement true or false? Epigenetics involves heritable, reversible modifications of DNA or histones that alter gene expression without changing the DNA sequence. A) The statement is false because epigenetic modifications are not heritable. B) The statement is false because epigenetic modifications are permanent. C) The statement is false because epigenetic modifications can change the DNA sequence. D) The statement is true.

D. The statement is true.

The lac operon repressor . . . A) requires cyclic AMP (cAMP) as a cofactor. B) binds to the promoter upstream of the lac structural genes. C) only binds to DNA when lactose is present. D) binds to the operator sequence when lactose is unavailable

D. binds to the operator sequence when lactose is unavailable

Oil content in sunflower seeds is controlled by five genes P-T, with each additive allele (designated by capital letters) adding 2% to the oil content above a baseline of 30% measured in plants with pp qq rr ss tt genotype. A plant of unknown genotype as an oil content of 46%. Which of the following is a possible genotype of that plant? A) Pp QQ RR Ss Tt B) PP QQ RR SS TT C) Pp Qq Rr Ss Tt D) pp QQ RR SS TT

D. pp QQ RR SS TT

For populations in Hardy-Weinberg equilibrium, the frequency of the recessive allele is represented as ________. A) 2pq. B) p2. C) p. D) q. E) q2.

D. q.

The stability/half-life of eukaryotic mRNAs is influenced by elements located in _____________. A) introns B) promoters C) the coding region of the mRNA D) the untranslated regions of the mRNA

D. the untranslated regions of the mRNA

Expression of the lac operon is highest . . . A) when neither glucose nor lactose is present. B) when glucose is present and lactose is absent. C) when both lactose and glucose are present. D) when lactose is present and glucose is absent.

D. when lactose is present and glucose is absent.

When a population is in Hardy-Weinberg equilibrium for alleles A and a, which of the following will be true of the population? A) The allele frequencies will remain constant from generation to generation. B) The genotypic frequencies can be predicted based on allele frequencies. C) The frequency of allele A will equal the frequency of allele a. D) The allele frequencies will change at a constant rate. E) Both A and B

E. Both A and B

In terms of population genetics, an allele that becomes "fixed" . . . A) reverts to the wild-type phenotype. B) has a frequency of 0. C) is the only allele of that gene present in the population. D) has a frequency of 1. E) Both C and D

E. Both C and D