Questions and Answers of Principles of Genetics

One strand of a gene in Arabidopsis thaliana has the following nucleotide
How might the absence of introns in a retroviral onco-gene explain that gene’s overexpression in the tissues of an infected animal?
How do we know that normal cellular oncogenes are not simply integrated retroviral oncogenes that have acquired the proper regulation?
Distinguish between therapeutic and reproductive cloning.
How might you show that two mouse Hoxgenes are expressed in different tissues and at different times dur-ing development?
How do the somatic cells that surround a developing Drosophilaegg in the ovary influence the formation of the dorsal–ventral axis in the embryo that will be pro-duced after the egg is fertilized?
The composite transposon Tn5 consists of two IS50 elements, one on either side of a group of three genes for antibiotic resistance. The entire unit IS50L kanr bler strr IS50R can transpose to a new
A population is segregating three alleles, A1, A2, and A3, with frequencies 0.2, 0.5, and 0.3, respectively. If these alleles are selectively neutral, what is the probability that A2 will ultimately
In a large population that reproduces by random mating, the frequencies of the genotypes GG, Gg, and gg are 0.04, 0.32, and 0.64, respectively. Assume that a change in the climate induces the
In a sample from an African population, the frequencies of the LM and LN alleles were 0.78 and 0.22, respectively. If the population mates randomly with respect to the M–N blood types, what are the
A study of quantitative variation for abdominal bristle number in female Drosophila yielded estimates of VT = 6.08, Vg = 3.17, and Ve = 2.91. What was the broad-sense heritability?
If heart disease is considered to be a threshold trait, what genetic and environmental factors might contribute to the underlying liability for a person to develop this disease?
Let’s check the Salk Institute’s Genome Analysis Laboratory web site (http://signal.salk.edu/cgi-bin/tdnaexpress) to see if any of their T-DNA lines have insertions in the gene shown in the
The sequence of a gene in Drosophila melanogaster that encodes a histone H2A polypeptide is as
Assume that you have just sequenced a small fragment of DNA that you had cloned. The nucleotide sequence of this segment of DNA is as
What is the major advantage of gene chips as a microarray hybridization tool?
Bacteriophage FX174 contains 11 genes in a genome of 5386 bp; E. coli has a predicted 4288 genes in a genome of about 4.639 kb; S. cerevisiae has about 6000 genes in a genome of size 12.1 mb; C.
You have identified a previously unknown human EST. What must be done before this new EST can be called an STS?
You have cloned a previously unknown human gene. What procedure will allow you to position this gene on the cytological map of the human genome without performing any pedigree analyses? Describe how
Ten micrograms of a decanucleotide-pair HpaI restriction fragment were isolated from the double-stranded DNA chromosome of a small virus. Octanucleotide poly(A) tails were then added to the
The automated DNA sequencing machines utilize fluorescent dyes to detect the nascent DNA chains synthesized in the presence of the four dideoxy (ddX) chain terminators, each labeled with a different
You are studying a circular plasmid DNA molecule of size 10.5 kilobase pairs (kb). When you digest this plasmid with restriction endonucleases BamHI, EcoRI, and HindIII, singly and in all possible
A DNA molecule is subjected to single and double digestions with restriction enzymes, and the products are separated by gel electrophoresis. The results are as follows (fragment sizes are in kb):Draw
A linear DNA molecule is subjected to single and double digestions with restriction endonucleases, and the following results are obtained:Draw the restriction map defined by these data. Fragment
Cereal grains are major food sources for humans and other animals in many regions of the world. However, most cereal grains contain inadequate supplies of certain of the amino acids that are
The cystic fibrosis (CF) gene (location: chromosome 7, region q31) has been cloned and sequenced, and studies of CF patients have shown that about 70 percent of them are homozygous for a mutant CF
In the following illustration, the upper line shows a gene composed of segments A€“D. The lower circle shows a mutant version of this gene, consisting of two fused pieces (A-B, C-D),
Bacteriophage MS2 carries its genetic information in RNA. Its chromosome is analogous to a polygenic molecule of mRNA in organisms that store their genetic information in DNA. The MS2 minichromosome
Are mutational changes induced by nitrous acid more likely to be transitions or transversions?
A cross was performed in Neurospora crassa between a strain of mating type A and genotype x+m+z and a strain of mating type a and genotype x m z+. Genes x, m, and z are closely linked and are present
The bacteriophage T4 genome contains about 50 percent A:T base pairs and 50 percent G:C base pairs. The base analog 2-aminopurine induces A:T → G:C and G:C → A:T base-pair substitutions by
If CTT is a DNA triplet (transcribed strand of DNA) specifying glutamic acid, what DNA and mRNA base triplet alterations could account for valine and lysine in position 6 of the b-globin chain?
In Drosophila, the Y chromosome Y·w+ has a small piece of the X chromosome translocated to it; this piece contains the wild-type alleles of all the genes missing in Df(1)wrJ1 mentioned in Problem
The deficiency Df(1)wrJ1 removes 16 contiguous bands from a region near the left end of the Drosophila X chromosome. Females homozygous for this deficiency die. However, females heterozygous for it
A mutator gene Dt in maize increases the rate at which the gene for colorless aleurone (a) mutates to the dominant allele (A), which yields colored aleurone. When reciprocal crosses were made (i.e.,
How could spontaneous mutation rates be optimized by natural selection?
How might enzymes such as DNA polymerase be involved in the mode of action of both mutator and antimutator genes (mutant genes that increase and decrease, respectively, mutation rates)?
If a single short-legged sheep should occur in a flock, suggest experiments to determine whether the short legs are the result of a mutation or an environmental effect. If due to a mutation, how can
Products resulting from somatic mutations, such as the navel orange and the Delicious apple, have become widespread in citrus groves and apple orchards. However, traits resulting from somatic
Juvenile muscular dystrophy in humans depends on an X-linked recessive gene. In an intensive study, 33 cases were found in a population of some 800,000 people. The investigators were confident that
What are the basic differences between translation in prokaryotes and in eukaryotes?
A precancerous condition (intestinal polyposis) in a particular human family group is caused by a single dominant gene. Among the descendants of one woman who died with cancer of the colon, 10 people
Published spontaneous mutation rates for humans are generally higher than those for bacteria. Does this indicate that individual genes of humans mutate more frequently than those of bacteria? Explain.
H. J. Muller used the ClB technique to identify many radiation-induced recessive lethal mutations on Drosophila’s X chromosome, which is now known to contain more than a thousand genes. These
Both lethal and visible mutations are expected to occur in fruit flies that are subjected to irradiation. Outline a method for detecting (a) X-linked lethals and (b) X-linked visible
Of all possible missense mutations that can occur in a segment of DNA encoding the amino acid tryptophan, what is the ratio of transversions to transitions if all single base-pair substitutions occur
Identify the following point mutations represented in DNA and in RNA as (1) transitions, (2) transversions, or (3) reading frameshifts. (a) A to G; (b) C to T; (c) C to G; (d) T
The following DNA sequence occurs in a bacterium (the promoter sequence is located to the left but is
Alan Garen extensively studied a particular nonsense (chain-termination) mutation in the alkaline phosphatase gene of E. coli. This mutation resulted in the termination of the alkaline phosphatase
The following DNA sequence occurs in the nontemplate strand of a gene in a bacterium (the promoter sequence is located to the left but is not shown):
A partial (5′ subterminal) nucleotide sequence of a prokaryotic mRNA is as follows:5′-.....AGGAGGCUCGAACAUGUCAAUAUGCUUGUUCCAAUCGUUAGCUGCGCAGGACCGUCCCGGA.. . . . . 3′When this mRNA is
The 5′ terminus of a human mRNA has the following sequence:5′-GAAGAGACAAGGTCAUGGCCAUAUGCUUGUUCCAAUCGUUAGCUGCGCAGGAUCGCCCUGGG. . . . . . 3′When this mRNA is translated, what amino acid sequence
(a) In what ways are ribosomes and spliceosomes similar?(b) In what ways are they different?
(a) What is the function of the Shine–Dalgarno sequence in prokaryotic mRNAs? (b) What effect does the deletion of the Shine–Dalgarno sequence from an mRNA have on its translation?
(a) In what ways does the order in the genetic code minimize mutational lethality? (b) Why do base-pair changes that cause the substitution of a leucine for a valine in the polypeptide gene
What are the functions of the A, P, and E aminoacyltRNA binding sites on the ribosome?
The human a-globin chain is 141 amino acids long. How many nucleotides in mRNA are required to encodehuman a-globin?
(a) What is the difference between a nonsense mutation and a missense mutation?(b) Are nonsense or missense mutations more frequent in living organisms?(c) Why?
An E. coli gene has been isolated and shown to be 68 nm long. What is the maximum number of amino acids that this gene could encode?
What is the function of each of the following components of the protein-synthesizing apparatus:(a) Aminoacyl-tRNA synthetase. (b) Release factor 1.(c) Peptidyl transferase. (d) Initiation
Assume that in the year 2025, the first expedition of humans to Mars discovers several Martian life forms thriving in hydrothermal vents that exist below the planet’s surface. Several teams of
The bases A, G, U, C, I (inosine) all occur at the 5′ positions of anticodons in tRNAs.(a) Which base can pair with three different bases at the 3′ positions of codons in mRNA? (b) What is
If the average molecular mass of an amino acid in a particular polypeptide is 100 daltons, about how many nucleotides will be present in an mRNA coding sequence specifying this polypeptide, which has
Of what significance is the wobble hypothesis?
How is translation (a) Initiated and (b) Terminated?
Outline the process of aminoacyl-tRNA formation.
(a) How is messenger RNA related to polysome formation? (b) How does rRNA differ from mRNA and tRNA in specificity? (c) How does the tRNA molecule differ from that of DNA and mRNA in size
Identify three different types of RNA that are involved in translation and list the characteristics and functions of each.
(a) Where in the cells of higher organisms do ribosomes originate?(b) Where in the cells are ribosomes most active in protein synthesis?
Characterize ribosomes in general as to size, location, function, and macromolecular composition.
What is the minimum number of tRNAs required to recognize the six codons specifying the amino acid leucine?
Using the information given in Problem 12.8, would you expect 5-bromouracil to induce a higher frequency of His → Arg or His → Pro substitutions? Why?
The thymine analog 5-bromouracil is a chemical mutagen that induces single base-pair substitutions in DNA called transitions (substitutions of one purine for another purine and one pyrimidine for
In what sense and to what extent is the genetic code:(a) Degenerate, (b) Ordered, and (c) Universal?
What types of experimental evidence were used to decipher the genetic code?
(a) Why is the genetic code a triplet code instead of a singlet or doublet code? (b) How many different amino acids are specified by the genetic code? (c) How many different amino acid
Why was it necessary to modify Beadle and Tatum’s one gene–one enzyme concept of the gene to one gene–one polypeptide?
Is the number of potential alleles of a gene directly related to the number of nucleotide pairs in the gene? Issuch a relationship more likely to occur in prokaryotes or in eukaryotes? Why?
At what locations in the cell does protein synthesis occur?
In a general way, describe the molecular organization of proteins and distinguish proteins from DNA, chemically and functionally. Why is the synthesis of proteins of particular interest to
Total RNA was isolated from nuclei of human cells growing in culture. This RNA was mixed with a purified, denatured DNA fragment that carried a large intron of a housekeeping gene (a gene expressed
A mutation in an essential human gene changes the 5′ splice site of a large intron from GT to CC. Predict the phenotype of an individual homozygous for this mutation.
How do the mechanisms by which the introns of tRNA precursors, Tetrahymena rRNA precursors, and nuclear pre-mRNAs are excised differ? In which process are snRNAs involved? What role(s) do these
How does RNA editing contribute to protein diversity in eukaryotes?
In what ways are most eukaryotic gene transcripts modified? What are the functions of these posttranscriptional modifications?
What two elements are almost always present in the promoters of eukaryotic genes that are transcribed by RNA polymerase II? Where are these elements located relative to the transcription start site?
Transcription and translation are coupled in prokaryotes. Why is this not the case in eukaryotes?
Total RNA was isolated from human cells growing in culture. This RNA was mixed with nontemplate strands (single strands) of the human gene encoding the enzyme thymidine kinase, and the RNA–DNA
What is the central dogma of molecular genetics? What impact did the discovery of RNA tumor viruses have on the central dogma?
A Drosophila second chromosome that carried a recessive lethal mutation, l(2)g14, was maintained in a stock with a balancer chromosome marked with a dominant mutation for curly wings. This latter
Two preparations of RNA polymerase from E. coli are used in separate experiments to catalyze RNA synthesis in vitro using a purified fragment of DNA carrying the argH gene as template DNA. One
Design an experiment to demonstrate that RNA transcripts are synthesized in the nucleus of eukaryotes and are subsequently transported to the cytoplasm.
Two eukaryotic genes encode two different polypeptides, each of which is 335 amino acids long. One gene contains a single exon; the other gene contains an intron of 41,324 nucleotide pairs long.
Why was the need for an RNA intermediary in protein synthesis most obvious in eukaryotes? How did researchers first demonstrate that RNA synthesis occurred in the nucleus and that protein synthesis
What five types of RNA molecules participate in the process of gene expression? What are the functions of each type of RNA? Which types of RNA perform their function(s) in (a) The nucleus and (b) The
Compare the structures of primary transcripts with those of mRNAs in prokaryotes and eukaryotes. On average, in which group of organisms do they differ the most?
What are the two stages of gene expression? Where do they occur in a eukaryotic cell? a prokaryotic cell?
What do processes of DNA synthesis, RNA synthesis, and polypeptide synthesis have in common?
The biosynthesis of metabolite X occurs via six steps catalyzed by six different enzymes. What is the minimal number of genes required for the genetic control of this metabolic pathway? Might more
The genome of a human must store a tremendous amount of information using the four nucleotide pairs present in DNA. What does the language of computers tell us about the feasibility of storing large

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