Questions and Answers of Principles of Genetics

The complete sequences of six mitochondrial genomes of H. neanderthalensis have been available for some time; the first H. neanderthalensis mtDNA sequence was published in 2008. How similar are the
The NCBI web site (http://www.ncbi.nlm.nih.gov) can also be used to search for protein sequences. Instead of performing a BLAST search with a nucleic acid query, one performs a protein blast with a
Many valuable human proteins contain carbohydrate or lipid components that are added posttranslationally. Bacteria do not contain the enzymes needed to add these components to primary translation
The CRISPR/Cas9 anti-phage immunity system in Streptococcus pyogenes deploys a variety of crRNAs derived from the spacer and repeat sequences in the CRISPR array in the S. pyogenes genome. In
Tropomyosins are proteins that mediate the interaction of actin and troponin, two proteins involved in muscle contractions. In higher animals, tropomyosins exist as a family of closely related
A researcher suspects that a 550-bp-long intron contains an enhancer that drives expression of an Arabidopsis gene specifically in root tip tissue. Outline an experiment to test this hypothesis.
A wheat variety with red kernels (genotype A′A′ B′B′) was crossed with a variety with white kernels (genotype AA BB). The F1 were inter crossed to produce an F2. If each primed allele
For alcoholism, the concordance rate for monozygotic twins is 55 percent, whereas for dizygotic twins, it is 28 percent. Do these data suggest that alcoholism has a genetic basis?
The height of the seed head in wheat at maturity is determined by several genes. In one variety, the head is just 9 inches above the ground; in another, it is 33 inches above the ground. Plants from
Assume that size in rabbits is determined by genes with equal and additive effects. From a total of 2012 F2 progeny from crosses between true-breeding large and small varieties, eight rabbits were as
A sample of 20 plants from a population was measured in inches as follows: 18, 21, 20, 23, 20, 21, 20, 22, 19, 20, 17, 21, 20, 22, 20, 21, 20, 22, 19, and 23.Calculate (a) The mean, (b) The
Quantitative geneticists use the variance as a measure of scatter in a sample of data; they calculate this statistic by averaging the squared deviations between each measurement and the sample mean.
Two inbred strains of corn were crossed to produce an F1, which was then intercrossed to produce an F2. Data on ear length from a sample of F1 and F2 individuals gave phenotypic variances of 15.2 cm2
A researcher has been studying kernel number on ears of corn. In one highly inbred strain, the variance for kernel number is 426. Within this strain, what is the broadsense heritability for kernel
Measurements on ear length were obtained from three populations of corn—two inbred varieties and a randomly pollinated population derived from a cross between the two inbred strains. The phenotypic
Summarizes data on maturation time in populations of wheat. Do these data provide any insight as to whether or not this trait is influenced by dominance? Explain.
A quantitative geneticist claims that the narrow-sense heritability for body mass in human beings is 0.7, while the broad-sense heritability is only 0.3. Why must there be an error?
The mean value of a trait is 100 units, and the narrowsense heritability is 0.4. A male and a female measuring 124 and 126 units, respectively, mate and produce a large number of offspring, which are
The narrow-sense heritability for abdominal bristle number in a population of Drosophila is 0.3. The mean bristle number is 12. A male with 10 bristles is mated to a female with 20 bristles, and a
A breeder is trying to decrease the maturation time in a population of sunflowers. In this population, the mean time to flowering is 100 days. Plants with a mean flowering time of only 90 days were
A fish breeder wishes to increase the rate of growth in a stock by selecting for increased length at 6 weeks after hatching. The mean length of 6-week-old fingerlings is currently 10 cm. Adult fish
On the basis of the observed correlations for personality traits shown in Table 19.5, what can you say about the value of the environmentality?
Leo’s IQ is 86 and Julie’s IQ is 110. The mean IQ in the population is 100. Assume that the narrow-sense heritability for IQ is 0.4. What is the expected IQ of Leo and Julie’s first child?
One way to estimate a maximum value for the narrowsense heritability is to calculate the correlation between half-siblings that have been reared apart and divide it by the fraction of genes that
A selection differential of 40 mg per generation was used in an experiment to select for increased pupa weight in Tribolium. The narrow-sense heritability for pupa weight was estimated to be 0.3. If
Correlations between relatives provide estimates of the broad and narrow-sense heritabilities on the assumption that the genetic and environmental factors influencing quantitative traits are
Female Drosophila heterozygous for three recessive mutations e (ebony body), st (scarlet eyes), and ss (spineless bristles) were testcrossed, and the following progeny were obtained:Phenotype
The following data for the M€“N blood types were obtained from native villages in Central and North America:Calculate the frequencies of the LM and LN alleles for the two groups. Group
The frequency of an allele in a large randomly mating population is 0.2. What is the frequency of heterozygous carriers?
The incidence of recessive albinism is 0.0004 in a human population. If mating for this trait is random in the population, what is the frequency of the recessive allele?
Human beings carrying the dominant allele T can taste the substance phenylthiocarbamide (PTC). In a population in which the frequency of this allele is 0.4, what is the probability that a particular
A gene has three alleles, A1, A2, and A3, with frequencies 0.6, 0.3, and 0.1, respectively. If mating is random, predict the combined frequency of all the heterozygotes in the population.
Hemophilia is caused by an X-linked recessive allele. In a particular population, the frequency of males with hemophilia is 1/4000. What is the expected frequency of females with hemophilia?
In Drosophila, the ruby eye phenotype is caused by a recessive, X-linked mutant allele. The wild-type eye color is red. A laboratory population of Drosophila is started with 25 percent ruby-eyed
A trait determined by an X-linked dominant allele shows 100 percent penetrance and is expressed in 36 percent of the females in a population. Assuming that the population is in Hardy–Weinberg
A phenotypically normal couple has had one normal child and a child with cystic fibrosis, an autosomal recessive disease. The incidence of cystic fibrosis in the population from which this couple
What frequencies of alleles A and a in a randomly mating population maximize the frequency of heterozygotes?
In an isolated population, the frequencies of the IA, IB, and i alleles of the A–B–O blood type gene are, respectively, 0.15, 0.25, and 0.60. If the genotypes of the A–B–O blood type gene are
In a survey of moths collected from a natural population, a researcher found 51 dark specimens and 49 light pecimens. The dark moths carry a dominant allele, and the light moths are homozygous for a
A population of Hawaiian Drosophila is segregating two alleles, P1 and P2, of the phosphoglucose isomerase (PGI) gene. In a sample of 100 flies from this population, 30 were P1P1 homozygotes, 60 were
The frequencies of the alleles A and a are 0.6 and 0.4, respectively, in a particular plant population. After many generations of random mating, the population goes through one cycle of
Each of two isolated populations is in Hardy€“Weinberg equilibrium with the genotype frequencies shown below:(a) If the populations are equal in size and they merge to form a single large
A population consists of 25 percent tall individuals (genotype TT), 25 percent short individuals (genotype tt), and 50 percent individuals of intermediate height (genotype Tt). Predict the ultimate
In controlled experiments with different genotypes of an insect, a researcher has measured the probability of survival from fertilized eggs to mature, breeding adults. The survival probabilities of
In a large randomly mating population, 0.84 of the individuals express the phenotype of the dominant allele A and 0.16 express the phenotype of the recessive allele a. (a) What is the frequency
Because individuals with cystic fibrosis die before they can reproduce, the coefficient of selection against them is s = 1. Assume that heterozygous carriers of the recessive mutant allele
For each set of relative fitnesses for the genotypes AA, Aa, and aa, explain how selection is operating. Assume that 0 < t < s < 1. AA Aa aa Case 1 1-s 1-s 1-s 1 1-t 1-s 1-s 1 Case 2 Case 3
The frequency of newborn infants homozygous for a recessive lethal allele is about 1 in 25,000. What is the expected frequency of carriers of this allele in the population?
A population of size 50 reproduces in such a way that the population size remains constant. If mating is random, how rapidly will genetic variability, as measured by the frequency of heterozygotes,
A small island population of mice consists of roughly equal numbers of males and females. The Y chromosome in one-fourth of the males is twice as long as the Y chromosome in the other males because
In some regions of west Africa, the frequency of the HBBS allele is 0.2. If this frequency is the result of a dynamic equilibrium due to the superior fitness of HBBSHBBA heterozygotes, and if
Mice with the genotype Hh are twice as fit as either of the homozygotes HH and hh. With random mating, what is the expected frequency of the h allele when the mouse population reaches a dynamic
A completely recessive allele g is lethal in homozygous condition. If the dominant allele G mutates to g at a rate of 10−6 per generation, what is the expected frequency of the lethal allele when
Individuals with the genotype bb are 20 percent less fit than individuals with the genotypes BB or Bb. If B mutates to b at a rate of 10−6 per generation, what is the expected frequency of the
Which of the following pairs of DNA sequences could qualify as the terminal repeats of a bacterial IS element. Explain.(a) 5′-GAATCCGCA-3′ and 5′-ACGCCTAAG-3′(b) 5′-GAATCCGCA-3′ and
Which of the following pairs of DNA sequences could qualify as target site duplications at the point of an IS50 insertion? Explain.(a) 5′-AATTCGCGT-3′ and 5′-AATTCGCGT-3′(b)
One strain of E. coli is resistant to the antibiotic streptomycin, and another strain is resistant to the antibiotic ampicillin. The two strains were cultured together and then plated on selective
What distinguishes IS and Tn3 elements in bacteria?
The circular order of genes on the E. coli chromosome is *A B C D E F G H*, with the * indicating that the ends of the chromosome are attached to each other. Two copies of an IS element are located
By chance, an IS1 element has inserted near an IS2 element in the E. coli chromosome. The gene between them, sug+, confers the ability to metabolize certain sugars. Will the unit IS1 sug+ IS2 behave
A researcher has found a new Tn5 element with the structure IS50L strr bler kanr IS50L. What is the most likely origin of this element?
Would a Tn3 element with a frameshift mutation early in the tnpA gene be able to form a cointegrate? Would a Tn3 element with a frameshift mutation early in the tnpR gene be able to form a
What enzymes are necessary for replicative transposition of Tn3? What are their respective functions?
What is the medical significance of bacterial transposons?
Describe the structure of the Ac transposon in maize. In what ways do the Ds transposons differ structurally and functionally from the Ac transposon?
In homozygous condition, a deletion mutation of the c locus, cn, produces colorless (white) kernels in maize; the dominant wild-type allele, C, causes the kernels to be purple. A newly identified
In maize, the O2 gene, located on chromosome 7, controls the texture of the endosperm, and the C gene, located on chromosome 9, controls its color. The gene on chromosome 7 has two alleles, a
In maize, the recessive allele bz (bronze) produces a lighter color in the aleurone than does the dominant allele, Bz. Ears on a homozygous bz/bz plant were fertilized by pollen from a homozygous
The X-linked singed locus is one of several in Drosophila that controls the formation of bristles on the adult cuticle. Males that are hemizygous for a mutant singed allele have bent, twisted
Dysgenic hybrids in Drosophila have elevated mutation rates as a result of P element transposition. How could you take advantage of this situation to obtain P element insertion mutations on the X
If DNA from a P element insertion mutation of the Drosophila white gene and DNA from a wild-type white gene were purified, denatured, mixed with each other, renatured, and then viewed with an
When complete Pelements are injected into embryos from an M strain, they transpose into the chromosomes of the germ line, and progeny reared from these embryos can be used to establish new P strains.
(a) What are retroviruslike elements? (b) Give examples of retroviruslike elements in yeast and Drosophila.(c) Describe how retroviruslike elements transpose.(d) After a retroviruslike element
Sometimes, solitary copies of the LTR of Ty1elements are found in yeast chromosomes. How might these soli-tary LTRs originate?
Would you ever expect the genes in a retrotransposon to possess introns? Explain.
Suggest a method to determine whether the TART retroposon is situated at the telomeres of each of the chromosomes in the Drosophilagenome.
It has been proposed that the hobotransposable elements in Drosophilamediate intrachromosomal recombination—that is, two hoboelements on the same chromosome pair and recombine with each other. What
What evidence suggests that some transposable elements are not simply genetic parasites?
Predict the phenotype of a fruit fly that develops from an embryo in which the posterior pole cells had been destroyed by a laser beam.
Approximately half of all spontaneous mutations in Dro-sophilaare caused by transposable element insertions. In human beings, however, the accumulated evidence sug-gests that the vast majority of
Z. Ivics, Z. Izsvák, and P. B. Hackett have “resurrected” a nonmobile member of the Tc1/marinerfamily of trans-posable elements isolated from the DNA of salmon. These researchers altered 12
The human genome contains about 5000 “processed pseudogenes,” which are derived from the insertion of DNA copies of mRNA molecules derived from many different genes. Predict the structure of
During oogenesis, what mechanisms enrich the cyto-plasm of animal eggs with nutritive and determinative materials?
Outline the main steps in the genetic analysis of development in a model organism such as Drosophila.
Why is the early Drosophilaembryo a syncytium?
In Drosophila, what larval tissues produce the external organs of the adult?
Like dorsal,bicoidis a strict maternal-effect gene in Dro-sophila; that is, it has no zygotic expression. Recessive mutations in bicoid(bcd) cause embryonic death by pre-venting the formation of
Why do women, but not men, who are homozygous for the mutant allele that causes phenylketonuria produce children that are physically and mentally retarded?
In Drosophila, recessive mutations in the dorsal–ventral axis gene dorsal(dl) cause a dorsalized phenotype in embryos produced by dl/dlmothers; that is, no ventral structures develop. Predict the
A researcher is planning to collect mutations in maternal-effect genes that control the earliest events in Drosophila development. What phenotype should the researcher look for in this search for
A researcher is planning to collect mutations in the gap genes, which control the first steps in the segmentation of Drosophilaembryos. What phenotype should the researcher look for in this search
What events lead to a high concentration of hunchback protein in the anterior of Drosophilaembryos?
Diagram a pathway that shows the contributions of the sevenless(sev) and bride of sevenless(boss) genes to the dif-ferentiation of the R7 photoreceptor in the ommatidia of Drosophilaeyes. Where would
The sevB4 allele is temperature sensitive; at 22.7°C, flies that are homozygous for it develop normal R7 photore-ceptors, but at 24.3°C, they fail to develop these photo-receptors. sos2A is a
When the mouse Pax6gene, which is homologous to the Drosophila eyelessgene, is expressed in Drosophila, it produces extra compound eyes with ommatidia, just like normal Drosophilaeyes. If the
Would you expect to find homologues of Drosophila’s BX-C and ANT-C genes in animals with radial symmetry such as sea urchins and starfish? How could you address this question experimentally?
What is the scientific significance of reproductive cloning?
The methylation of DNA, the acetylation of histones, and the packaging of DNA into chromatin by certain kinds of proteins are sometimes referred to as epigenetic modifications of the DNA. These
Assume that an animal is capable of producing 100 mil-lion different antibodies and that each antibody contains a light chain of 220 amino acids long and a heavy chain of 450 amino acids. How much
Each L4V4 segment in the kappa light chain locus on chromosome 2 consists of two coding exons, one for the leader peptide and one for the variable portion of the kappa light chain. Would you expect

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