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Genetics Final Exam

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Kocher, Thomas. University of MD, College Park. Genetics Final Exam Review Fall 2016
Engela Zalmy
Quiz by Engela Zalmy, updated more than 1 year ago
Engela Zalmy
Created by Engela Zalmy over 7 years ago
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Question 1

Question
The full chemical name of DNA is [blank_start]deoxyribonucleic acid[blank_end] .
Answer
  • deoxyribonucleic acid

Question 2

Question
The protein, [blank_start]primase[blank_end], is needed to lay down a segment of RNA complementary to the DNA before replication can begin.
Answer
  • primase

Question 3

Question
An origin of replication generally has [blank_start]two[blank_end] (how many?) replication forks.
Answer
  • two

Question 4

Question
The discontinuous lagging strand on a replication fork consists of [blank_start]Okazaki fragments[blank_end] that are later ligated together to form one strand of DNA.
Answer
  • Okazaki fragments

Question 5

Question
The E. coli chromosome contains [blank_start]one[blank_end] (how many?) origin(s) of replication?
Answer
  • one

Question 6

Question
A prokaryote lacks a [blank_start]nuclear[blank_end] membrane.
Answer
  • nuclear

Question 7

Question
Recombination is probably always initiated by [blank_start]nicking[blank_end] of DNA.
Answer
  • nicking

Question 8

Question
The [blank_start]leading[blank_end] strand is synthesized continuously during DNA replication.
Answer
  • leading

Question 9

Question
A [blank_start]restriction[blank_end] enzyme recognizes a specific DNA sequence and is able to cleave the DNA generating either “blunt” or “sticky” ends of the DNA.
Answer
  • restriction

Question 10

Question
A virus that infects bacterial cells is called a [blank_start]bacteriophage[blank_end].
Answer
  • bacteriophage

Question 11

Question
The genetic material of some viruses such as pi X 174 and M13 is [blank_start]single-stranded DNA[blank_end].
Answer
  • single-stranded DNA

Question 12

Question
The genetic material of the viruses that cause polio and AIDS is [blank_start]RNA[blank_end] .
Answer
  • RNA

Question 13

Question
Topoisomerase [blank_start]relaxes[blank_end] supercoils by nicking the DNA.
Answer
  • relaxes

Question 14

Question
In E. coli, recombination begins at [blank_start]chi[blank_end] sites where recBCD nicks and displaces a strand.
Answer
  • chi

Question 15

Question
Which of the following is not true of DNA?
Answer
  • It is acidic.
  • It contains deoxyribose.
  • It is found in cell nuclei.
  • It contains phosphate.
  • It contains proteins.

Question 16

Question
The molecule of heredity is:
Answer
  • RNA
  • DNA
  • protein
  • carbohydrate
  • none of the above

Question 17

Question
The four subunits which compose DNA are called:
Answer
  • phosphodiesters
  • proteins
  • nucleotides
  • nucleosides
  • polymers

Question 18

Question
DNA is localized mainly in the
Answer
  • cell membrane
  • endoplasmic reticulum
  • vacuoles
  • chromosomes
  • None of the above

Question 19

Question
Each nucleotide of DNA is made up of:
Answer
  • a deoxyribose sugar
  • a nitrogenous base
  • a phosphate
  • A and B only
  • All of the above

Question 20

Question
The polarity of DNA synthesis is:
Answer
  • 5' → 3'
  • 3' → 5'
  • 5' → 2'
  • 2' → 5'
  • none of the above

Question 21

Question
In the Hershey and Chase experiment designed to determine the molecule of heredity, what was radiolabeled with 35-S?
Answer
  • protein
  • DNA
  • RNA
  • rRNA
  • none of the above

Question 22

Question
The ratio of _____ is 1:1.
Answer
  • guanine to adenine
  • adenine to thymine
  • cytosine to adenine
  • uracil to cytosine
  • none of the above

Question 23

Question
X-ray data showed that the spacing between repeating units along the axis of the DNA helix is:
Answer
  • 2.0 angstroms.
  • 3.4 angstroms.
  • 20 angstroms.
  • 34 angstroms.
  • none of the above

Question 24

Question
X-ray data showed that the DNA helix undergoes one complete turn every:
Answer
  • 2.0 angstroms.
  • 3.4 angstroms.
  • 20 angstroms.
  • 34 angstroms.
  • none of the above

Question 25

Question
________ bonds are responsible for the chemical affinity between A and T (or G and C) nucleotides.
Answer
  • Ionic
  • Covalent
  • Hydrogen
  • Electro-ionic
  • none of the above

Question 26

Question
_______ -form DNA spirals to the right and is the major form of naturally occurring DNA molecules.
Answer
  • A
  • B
  • D
  • Y
  • Z

Question 27

Question
The nucleotide that is present in RNA but not DNA is:
Answer
  • thymine
  • uracil
  • adenine
  • cytosine
  • guanosine

Question 28

Question
DNA replication occurs through a _________process.
Answer
  • conservative
  • semiconervative
  • dispersive
  • transferal
  • none of the above

Question 29

Question
During complementary base pairing, enzymes join the base's nucleotide to the preceding nucleotide by a __________bond.
Answer
  • Hydrogen
  • Ionic
  • Phosphodiester
  • Electrostatic
  • None of the above

Question 30

Question
During early interphase the state of the DNA can be described as:
Answer
  • a single continuous linear double helix.
  • a double helix replicated semiconservatively.
  • a double helix replicated conservatively.
  • single-stranded DNA.
  • None of the above

Question 31

Question
During the S phase of interphase, the state of the DNA can be described as:
Answer
  • a single continuous linear double helix.
  • a double helix replicated semiconservatively.
  • a double helix replicated conservatively.
  • a triple helix replicated semiconservatively.
  • None of the above

Question 32

Question
The step in DNA replication in which the replication proteins open up the double helix and prepare for complementary base pairing is called:
Answer
  • Initiation
  • Elongation
  • Termination
  • Translation
  • Translocation

Question 33

Question
The step in DNA replication in which the proteins connect the correct sequence of nucleotides into a continuous new strand is called:
Answer
  • Initiation
  • Elongation
  • Termination
  • Translation
  • Translocation

Question 34

Question
The step in DNA replication in which two replication forks moving in opposite directions may meet is called:
Answer
  • Intiation
  • Elongation
  • Termination
  • Translation
  • Translocation

Question 35

Question
The group of enzymes able to relax supercoils in DNA is called:
Answer
  • Primases
  • Helicases
  • Topoisomerases
  • Telomeres
  • Ligases

Question 36

Question
How many replication forks depart from an origin of replication?
Answer
  • one
  • two
  • three
  • four
  • none of the above

Question 37

Question
The protein that progressively unwinds DNA ahead of each replication fork is called:
Answer
  • Primase
  • Helicase
  • Topoisomerase
  • Telomerase
  • Ligase

Question 38

Question
In eukaryotic cells, replication proceeds from ____ origin(s) of replication.
Answer
  • no
  • one
  • two
  • several
  • many

Question 39

Question
Eukaryotic chromosomes have evolved special structures at the ends of chromosomes to ensure the replication of the two ends of linear chromosomes. These structures are
Answer
  • methylases
  • capping proteins
  • ligases
  • telomerases
  • single-stranded binding proteins

Question 40

Question
Which of the following is NOT involved in ensuring the accuracy of a cell's genetic information?
Answer
  • redundancy
  • repair enzymes
  • precision of replication machinery
  • DNA polymerase proofreading mechanism
  • Restriction endonucleases

Question 41

Question
The process of _________ is extremely important in generating genetic diversity.
Answer
  • Translation
  • Transcription
  • Recombination
  • Transformation
  • None of the above

Question 42

Question
Any deviation from the expected 2:2 segregation of parental alleles that results from recombination is known as:
Answer
  • Allelic exchange
  • Gene conversion
  • Crossing over
  • Recombination
  • DNA replication

Question 43

Question
Recombination involves the breakage and reunion of DNA molecules from:
Answer
  • homologous nonsister chromatids
  • homologous sister chromatids
  • heterologous nonsister chromatids
  • heterologous sister chromatids
  • None of the above

Question 44

Question
The nicking of DNA that initiates recombination during mitosis may be due to all but:
Answer
  • instruction from normal cell-cycle program
  • X-rays
  • Chemical change
  • Physical change
  • Radiation

Question 45

Question
What radiolabeled substance did Hershey and Chase use to label the protein component of the bacteriophage in their study to determine whether protein or DNA was necessary for phage production?
Answer
  • nitrogen
  • carbon
  • sulfur
  • phosphorous
  • iodide

Question 46

Question
If 35% of the bases in a region of the mouse genome are cytosine, what percentage in that region are adenine?
Answer
  • 15%
  • 20%
  • 30%
  • 35%
  • none of the above

Question 47

Question
The complementary sequence of 5' AATTCGCTTA 3' is:
Answer
  • 5' AATTCGCTTA 3'
  • 3' AATTCGCTTA 5'
  • 5' TAACGCTTAA 3'
  • 5' TAAGCGAATT 3'
  • 3' TAAGCGAATT 5'

Question 48

Question
Two strains of S. cerevisae (yeast) are crossed. One has the genotype ABC and the other abc. Five sets of the resultant tetrads are noted below. In which set did a gene conversion event occur?
Answer
  • abc, aBc, AbC, aBC
  • abc, abc, ABC, ABC
  • aBc, aBc, AbC, AbC
  • abC, abc, ABc, ABC
  • Abc, Abc, aBC, aBC

Question 49

Question
Recombination occurs during meiotic ________.
Answer
  • anaphase
  • interphase
  • prophase
  • metaphase
  • none of the above

Question 50

Question
Without __________ regions on the DNA during recombination, gene conversion could not occur.
Answer
  • homoduplex
  • heteroduplex
  • homotriplex
  • heterotriplex
  • none of the above

Question 51

Question
Occasionally, a loss of function mutation may occur in the telomerase enzyme in a cell. What is likely to be the result of this mutation on the DNA in the cell over the the course of several rounds of mitosis?
Answer
  • chromosome length will gradually increase
  • chromosome length will gradually decrease
  • chromosome length will stay constant
  • chromosomes will fail to dissociate after replication
  • none of the above

Question 52

Question
Bacterial DNA is resistant to degradation by its own restriction enzymes through the protection of:
Answer
  • Methylases
  • Recombinases
  • Topoisomerases
  • Ligases
  • Primases

Question 53

Question
Hershey and Chase relied on ________ to physically separate the infected bacterial cells from the phage ghosts.
Answer
  • radioactivity
  • gel filtration
  • ion exchange
  • centrifugation
  • none of the above

Question 54

Question
Meselson and Stahl relied on equilibrium density gradient centrifugation in a _______ solution to resolve the DNA containing 14N from the DNA containing 15-N.
Answer
  • radiolabeled phosphate
  • calcium chloride
  • radiolabeled nitrogen
  • sodium acetate
  • cesium chloride

Question 55

Question
Match the scientist with their contribution to understanding more about DNA a. early recombination models b. transformation c. semiconservative replication d. x-ray structure of DNA e. revised recombination models f. basic structure of DNA g. DNA = molecule of heredity h. discovery of “nuclein” i. nucleotide ratios in DNA j. famous phage blender experiment 55. [blank_start]f[blank_end] Watson and Crick 56. [blank_start]i[blank_end] Chargaff 57. [blank_start]d[blank_end] Franklin and Wilkins 58. [blank_start]b[blank_end] Griffith 59. [blank_start]j[blank_end] Hershey and Chase 60. [blank_start]h[blank_end] Miescher 61. [blank_start]c[blank_end] Meselson and Stahl 62. [blank_start]a[blank_end] Holliday 63. [blank_start]e[blank_end] Meselson and Radding 64. [blank_start]g[blank_end] Avery, MacLeod and McCarty
Answer
  • f
  • i
  • d
  • b
  • j
  • h
  • c
  • a
  • e
  • g

Question 56

Question
Diagram Matching (Match the region or item on the diagram with the correct term from the list below) -lagging strand -leading strand -origin -RNA primer -Okazaki fragment -helicase -polymerase
Image:
090b3817-6143-4746-844a-92e664c88b07 (image/png)
Answer
  • leading strand
  • Okazaki fragment
  • RNA primer
  • helicase
  • polymerase
  • origin
  • lagging strand

Question 57

Question
A phosphodiester bond joins one nucleotide together in the DNA polymer.
Answer
  • True
  • False

Question 58

Question
Prokaryotes have a circular chromosome surrounded by a nuclear membrane.
Answer
  • True
  • False

Question 59

Question
Transformation in bacteria results from the uptake of foreign DNA.
Answer
  • True
  • False

Question 60

Question
DNA is highly negatively charged throughout the molecule and therefore has no
Answer
  • True
  • False

Question 61

Question
A region of DNA 100 bp in length has the potential to be represented by 4100 unique sequences.
Answer
  • True
  • False

Question 62

Question
Viruses use only DNA as their genetic material.
Answer
  • True
  • False

Question 63

Question
Restriction enzymes are molecular weapons which cut DNA that bacteria use in their fight to protect themselves from DNA viruses.
Answer
  • True
  • False

Question 64

Question
Human DNA is replicated in a conservative manner.
Answer
  • True
  • False

Question 65

Question
In DNA replication, new DNA is produced in a continuous bi-directional fashion.
Answer
  • True
  • False

Question 66

Question
DNA topoisomerase supercoils DNA to get it out of the way of DNA polymerase.
Answer
  • True
  • False

Question 67

Question
Accuracy of replication is enhanced by the redundancy of DNA, enzymatic repair of damaged DNA and the remarkable precision of the cellular replication machinery.
Answer
  • True
  • False

Question 68

Question
A 2:2 segregation of parental alleles is known as gene conversion.
Answer
  • True
  • False

Question 69

Question
Recombination events are limited to only “hot spots” along a chromosome.
Answer
  • True
  • False

Question 70

Question
Gene conversion in which a small segment of information from one homologous chromosome transfers to the other can give rise to an unequal yield of two different alleles.
Answer
  • True
  • False

Question 71

Question
Alternative resolutions of the Holliday intermediate are responsible for whether or not crossing over or gene conversion occurs.
Answer
  • True
  • False

Question 72

Question
Genes that “travel” together from one generation to the next more often than not exhibit [blank_start]genetic linkage[blank_end] .
Answer
  • genetic linkage

Question 73

Question
A probability test that measures “goodness of fit” between observed and predicted results is a [blank_start]chi squared[blank_end] test.
Answer
  • chi squared

Question 74

Question
A hypothesis that predicts no linkage between genes is called the [blank_start]null[blank_end] hypothesis.
Answer
  • null

Question 75

Question
Genes that can serve points of reference on a chromosome are useful as genetic markers while cytologically visible abnormalities that also make it possible to keep track of chromosomes are called [blank_start]physical[blank_end] markers.
Answer
  • physical

Question 76

Question
The movement of chiasmata toward the end of a chromosome is called [blank_start]terminalization[blank_end] .
Answer
  • terminalization

Question 77

Question
One percentage point of recombination, or recombination frequency, is a unit of measure called either centimorgan or [blank_start]map unit[blank_end] .
Answer
  • map unit

Question 78

Question
Crossovers do not occur independently and the occurrence of one crossover reduces the likelihood of another occurring elsewhere on the chromosome this is called [blank_start]chromosomal interference[blank_end] .
Answer
  • chromosomal interference

Question 79

Question
A tetrad that contains four recombinant class haploid cells is known as a [blank_start]non-parental[blank_end] ditype.
Answer
  • non-parental

Question 80

Question
A tetrad that carries four kinds of haploid cells: two different parental and two different recombinant class spores is referred to as [blank_start]tetratype[blank_end].
Answer
  • tetratype

Question 81

Question
Mistakes in mitosis during development often result in [blank_start]mosaic[blank_end] organisms containing tissues of different genotypes.
Answer
  • mosaic

Question 82

Question
The R/r and S/s genes are linked and 10 map units apart. In the cross Rs/rS  rs/rs what fraction of the progeny will be RS/rs?
Answer
  • 5%
  • 10%
  • 25%
  • 40%
  • 45%

Question 83

Question
If the map distance between genes A and B is 10 map units and the map distance between genes B and C is 25 map units, what is the map distance between genes A and C?
Answer
  • 15 map units
  • 35 map units
  • Either 15 map units or 35 map units, depending on the order of the genes
  • The map distance between A and C can not be predicted from this data

Question 84

Question
In Drosophila, singed bristles (sn) and cut wings (ct) are both caused by recessive, X-linked alleles. The wild type alleles (sn+ and ct+) are responsible for straight bristles and intact wings, respectively. A female homozygous for sn and ct+ is crossed to a sn+ct male. The F1 flies are interbred. The F2 males are distributed as follows: sn ct 13 sn ct+ 36 sn+ ct 39 sn+ ct+ 12 What is the map distance between sn and ct?
Answer
  • 12 m.u.
  • 13 m.u.
  • 25 m.u.
  • 50 m.u.
  • 75 m.u.

Question 85

Question
What is the value of X2 for a test of the hypothesis that the sn and car genes are unlinked?
Image:
7c8c5804-d2a0-41b6-9e32-d2fdc73bdf75 (image/png)
Answer
  • 0.5
  • 1.0
  • 2.0
  • 0.4
  • 20

Question 86

Question
What is the p value from this test? (Pick the most accurate choice.)
Image:
cd19a13a-928a-400f-a034-795843ca4107 (image/png)
Answer
  • p > 0.5
  • 0.5 > p > 0.1
  • p < 0.1
  • p < 0.05
  • p < 0.01

Question 87

Question
Suppose the L and M genes are on the same chromosome but separated by 100 map units. What fraction of the progeny from the cross LM/lm x lm/lm would be Lm/lm?
Answer
  • 10%
  • 25%
  • 50%
  • 75%
  • 100%

Question 88

Question
The pairwise map distances for four linked genes are as follows: A-B = 22 m.u., B-C = 7 m.u., C-D = 9 m.u., B-D = 2 m.u., A-D = 20 m.u., A-C = 29 m.u. What is the order of these four genes?
Answer
  • ABCD
  • ADBC
  • ABDC
  • BADC
  • CADB

Question 89

Question
The zipper-like connection between paired homologs in early prophase is known as a:
Answer
  • spindle fiber
  • synaptic junction
  • synaptomnemal complex
  • chiasma
  • none of the above

Question 90

Question
The measured distance between genes D and E in a two point test cross is 50 map units. What does this mean in physical terms?
Answer
  • D and E are on different pairs of chromosomes.
  • D and E are linked and exactly 50 map units apart.
  • D and E are linked and at least 50 map units apart.
  • either A or B
  • either A or C

Question 91

Question
Suppose an individual is heterozygous for a pair of alleles (e.g. A/a). Under what conditions would a crossover in a somatic cell of this individual lead to a clone of cells homozygous for a? (Pick the most precise answer.)
Answer
  • The crossover would have to occur between the A locus and the centromere and involve two homologous (non-sister) chromatids.
  • The crossover would have to occur between the A locus and the end of the chromosome and involve two homologous (non-sister) chromatids.
  • The crossover would have to occur on the same chromosome arm as the A locus and involve two homologous (non-sister) chromatids.
  • The crossover would have to occur on the same chromosome as the A locus and involve two homologous (non-sister) chromatids.
  • The crossover would have to occur between the A locus and the centromere and involve two sister chromatids (not homologous) chromatids.

Question 92

Question
Suppose an individual is heterozygous for two linked pairs of alleles on the same chromosome arm, Ab/aB such that the A locus is closer to the centromere than the B locus. Under what conditions would a crossover in a somatic cell generate a twin spot, i.e. two adjacent clones of cells, one clone homozygous for a and the other clone homozygous for b?
Answer
  • The crossover would have to occur between the A locus and the centromere locus and involve two homologous (non-sister) chromatids.
  • The crossover would have to occur between the A locus and the B locus locus and involve two homologous (non-sister) chromatids.
  • The crossover would have to occur between the B locus and the end of the chromosome locus and involve two homologous (non-sister) chromatids.
  • A double crossover would have to occur, with one crossover between the A locus and the centromere and a second crossover between the A and B loci locus and both crossovers would have to involve two homologous (non-sister) chromatids.
  • No crossover in a somatic cell could generate a twin spot.

Question 93

Question
What happens physically during the process of crossing over?
Answer
  • Two homologous chromatids break and rejoin at random sites along the chromosome.
  • The genetic information on one chromatid is replaced by copying genetic information from a homologous chromatid without there being any physical exchange between the chromosomes.
  • Two homologous chromatids break and rejoin at precisely the same site along the chromosome so that there is no loss or gain of material on either product.
  • It is not known what occurs during crossing over.

Question 94

Question
Here is a list of events during meiosis I. It is not in the correct order. A) Homologous chromosomes are roughly aligned but not physically linked. B) Homologous chromosomes segregate to opposite poles. C) Homologous chromosomes are linked by synaptonemal complexes. D) Homologous chromosomes are linked by chiasmata. E) Chromosomes replicate. What is the correct order of these events?
Answer
  • ACDBE
  • AECDB
  • EACDB
  • EADCB
  • CDABE

Question 95

Question
Some of the larger human chromosomes typically contain multiple chiasmata during meiotic prophase. If you were to carefully study the distribution of these chiasmata, what would you find?
Answer
  • Chiasmata are randomly distributed along chromosomes.
  • All chromosome pairs have the same number of chiasmata.
  • A single chromosome pair always has the same number of chiasmata in every meiotic cell.
  • Chiasmata are spaced along a chromosome arm more regularly than would be expected by chance.
  • Chiasmata are spaced more irregularly along a chromosome arm than would be expected by chance.

Question 96

Question
Recombination due to crossing over occurs only rarely in mitosis.
Answer
  • True
  • False

Question 97

Question
When considering the chi-square test, a p-value of 0.05 is often considered significant but is actually an arbitrary assignment of significance.
Answer
  • True
  • False

Question 98

Question
Chiasmata are structures of cross over between sister chromatids of homologous chromosomes.
Answer
  • True
  • False

Question 99

Question
Chiasmata can be seen through a light microscope and are sites of recombination.
Answer
  • True
  • False

Question 100

Question
Three-point crosses are more tedious and less accurate than two-point crosses.
Answer
  • True
  • False

Question 101

Question
Chromosomal interference is not uniform and may significantly vary within a region of a single chromosome.
Answer
  • True
  • False

Question 102

Question
Genetic mapping distance calculated for a chromosome is directly related to physical distance along that chromosome.
Answer
  • True
  • False

Question 103

Question
Genes chained together by linkage relationships are known collectively as a linkage group.
Answer
  • True
  • False

Question 104

Question
Ascospores are haploid cells that can germinate, replicate by mitosis, and survive as haploid individuals.
Answer
  • True
  • False

Question 105

Question
The Hardy-Weinberg equilibrium principle yields which of the following conclusions?
Answer
  • If the allele frequencies in a population are given by p and q, the genotype frequencies are given by p2, 2 pq and q2.
  • The allele frequencies in a population will not change over time.
  • If the allele frequencies in a population are given by p and q, the genotype frequencies are given by p2 and q2. d. The first and third answers are correct.
  • The first and second choices are correct.

Question 106

Question
The HIV epidemic is unlikely to lead to an increase in the CCR5 delta-32 allele over the short term because ___________________.
Answer
  • In populations with high selection pressure, the allele frequency is low.
  • the allele is recessive and deleterious.
  • The first and second choices are correct.
  • in populations with a high frequency of the allele, selection pressure is relatively low.

Question 107

Question
Over the long term, selection favoring the rare phenotype in a polymorphic population (i.e., negative frequency dependent selection), will __________ genetic diversity in the population.
Answer
  • decrease
  • increase
  • maintain

Question 108

Question
Which of these statements is true for underdominance?
Answer
  • Allele frequencies will tend to move towards fixation or loss.
  • Allele frequencies will tend to move toward a stable equilibrium.
  • Allele frequencies may initially hover at an unstable equilibrium, but will eventually change.

Question 109

Question
When selection acts against a recessive allele that is initially at high frequency in a population, ____________________.
Answer
  • the frequency of the allele will stay high for a long time, then decline slowly.
  • the allele declines in frequency until it is eliminated.
  • the frequency of the allele will be unchanged;
  • the population will remain in Hardy-Weinberg equilibrium. the frequency of the allele will decline rapidly, and then stabilize at very low frequency.

Question 110

Question
When selection favors heterozygotes over homozygotes, ____________________.
Answer
  • both alleles are maintained at a frequency different from that predicted by Hardy-Weinberg principles based on the strength of selection against the recessive allele.
  • the selective advantage enjoyed by the deleterious allele in the heterozygote exactly
  • genetic diversity in the population can be maintained indefinitely, in spite of selection acting against the allele. balances the selective disadvantage suffered by homozygous recessive individuals.
  • The first two choices are both correct.
  • The first three choices are correct.

Question 111

Question
When selection favors homozygotes over heterozygotes ____________________.
Answer
  • genetic variation among populations will decline.
  • the most common outcome will be that the most common allele will become fixed (will increase to a frequency of 1) in the population.
  • both alleles are maintained in the population at frequencies different from those predicted by Hardy-Weinberg principles.
  • the genetic variation within a population is maintained over time

Question 112

Question
Pier and his colleagues have suggested that cystic fibrosis is maintained at relatively high levels in people of European ancestry because of heterozygote superiority; specifically, he proposposes that heterozygotes are more resistant to typhoid fever than are the dominant homozygotes. Evidence in favor of this hypothesis includes which of the following findings?
Answer
  • The mutation rate for new loss-of-function mutations in the CFTR gene is too low for the prevalence of the disease to be explained by mutation/selection balance.
  • Pier and his colleagues have found, in 11 European countries, an association between the severity of typhoid fever outbreaks and the frequency of the delta-F508 allele (the most common loss-of-function mutation) a generation later.
  • Pier et al. engineered cells homozygous for functional CFTR alleles, homozygous for a common loss-of-function allele, and heterozygous for the two. The loss-of-function homozygotes were virtually impervious to invasion by typhoid fever-causing bacteria; heterozygotes were more vulnerable, but accumulated 86% fewer bacteria than did the dominant homozygotes.
  • All of the choices above are correct.
  • Salmonella typhi bacteria manipulate their host cells, causing them to express more CFTR protein on their membranes.
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