Deck 10: The Integration of Genetic Approaches: Understanding Sickle Cell Disease

Question 1

Which of the following techniques describes either the rate of a molecule's migration or its final position in a gel?

A)hybridization
B)electrophoretic mobility
C)densitometry
D)restriction fragment analysis
E)peptide fingerprint analysis

Answer 1

B

Question 2

Given what you know of the inheritance pattern of SCD,what can be said of individual II-5?

A)He is a carrier because his mother was affected and his son was affected.
B)He is unaffected,and the mutant allele is passed from II-4 to their son.
C)His children with II-4 will all have a 50% chance of being affected (βˢβˢ).
D)He is a carrier,and his children with II-4 will have a 50% chance of being affected (βˢβˢ)and a 50% chance of being a carrier (βᴬβˢ).
E)He is a carrier,and his children with II-4 will have a 50% chance of being affected (βˢβˢ)and a 50% chance of being unaffected (βᴬβᴬ).

Answer 2

D

Question 3

Sickle cell is a codominant disease,meaning that heterozygotes exhibit an intermediate blood cell phenotype (a mixture of normal and sickle cells)due to the blend of hemoglobin tetramers in each red blood cell.Which of the following tetramer structures would you expect to find in a carrier of SCD?

A)α₂βᴬ₂
B)α₂βˢβᴬ
C)α₂βˢ₂
D)α₂βᴬ₂ and α₂βˢβᴬ
E)α₂βᴬ₂ and α₂βˢβᴬ and α₂βˢ₂

Answer 3

E

Question 4

Molecular charge is an important characteristic influencing protein migration on a gel.What accounts for the variation in the molecular charge of proteins?

A)the intronic sequences of the protein
B)the amino acid composition of the protein
C)the negative charge of the sugar-phosphate backbone
D)the amount of protein loaded into the wells of the gel
E)the presence of secondary structures in the protein

Question 5

The mutation that causes SCD causes what kind of change in the structure of hemoglobin?

A)decreases heme-binding ability
B)fewer chains of amino acids (trimeric rather than tetrameric structure)
C)a single amino acid substitution that alters the structure of the tetramer
D)addition of a single amino acid that causes a longer protein subunit
E)loss of a single amino acid that causes a frameshift and premature stop codon

Question 6

The βˢ and βᴬ alleles can be distinguished on the basis of

A)variations in the length of their DNA restriction fragments.
B)variations in the length of the amino acid sequence.
C)different electrophoretic mobilities caused by a single amino acid substitution.
D)variations in the length of both the DNA restriction fragments and the amino acid sequence.
E)variations in the DNA restriction fragments and different electrophoretic mobilities of the protein products due to a single amino acid substitution.

Question 7

From a standpoint of natural selection,we see that the heterozygous advantage for βᴬβˢ individuals is balanced by the disadvantage to those with SCD or the wild-type alleles (and no malaria protection).The action of these conflicting trends produces an overall increase in the mutant allele until it reaches a state where the gain and loss of βˢ alleles is equal.What is the term for this stable condition that allows mutant alleles to remain in a particular population?

A)equilibrium frequency
B)heterozygote fitness
C)restriction fragment length polymorphism
D)single nucleotide polymorphism
E)balanced polymorphism

Question 8

The same DNA probe used to measure mRNA levels by northern blotting can also be used on a Southern blot with a restriction digest of genomic DNA.What new information can be gained from Southern blotting (that wasn't already obtained by the northern blot analysis)?

A)the level of protein that is being translated from the mRNA transcript
B)the presence of a unique restriction fragment pattern indicating a mutation in a known restriction site
C)the size of the genomic DNA fragments,including both introns and exons
D)the size of the genomic DNA fragments and the level of protein being translated
E)the size of the genomic DNA fragments and the presence of a unique restriction fragment pattern indicating a mutation in a known restriction site

Question 9

Pauling used gel electrophoresis to confirm that homozygous individuals produce a single form of β-globin protein that differs depending on the homozygous genotype as well as that heterozygotes produce proteins of both types in approximately equal concentration.What characteristic(s)of the bands proved this?

A)the positions of the protein bands
B)the densitometry peaks of each band
C)the shape of each band
D)both the positions and the densitometry peaks of each band
E)both the shape and the position of each band

Question 10

Given what you know of the inheritance pattern of SCD,is the following pedigree representative of a typical SCD pedigree?

A)Yes;this is a dominant pedigree,and SCD exhibits dominant inheritance.
B)Yes;this is a recessive pedigree,and SCD exhibits recessive inheritance.
C)No;this is a dominant pedigree,and SCD exhibits recessive inheritance.
D)No;this is a recessive pedigree,and SCD exhibits dominant inheritance.
E)Another generation is needed before you can determine mode of inheritance.

Question 11

What term is used to describe the situation when the loss of an allele because of selection against one of its phenotypes is balanced by natural selection in favor of the allele for another phenotype?

A)equilibrium frequency
B)heterozygote fitness
C)restriction fragment length polymorphism
D)single nucleotide polymorphism
E)balanced polymorphism

Question 12

How is gel electrophoresis used to demonstrate the molecular basis of SCD?

A)by revealing that the protein products of the βᴬ and βˢ alleles have distinctive electrophoretic band patterns
B)by revealing variations in the length of a DNA restriction fragment that distinguishes the βᴬ and βˢ alleles
C)by revealing variations in the exon splicing of the mRNA products of the βᴬ and βˢ alleles
D)by revealing variations in the electrophoretic mobility of proteins and the restriction fragment length polymorphisms of DNA
E)by revealing variations in the electrophoretic mobility of proteins,the restriction fragment length polymorphisms of DNA,and the splice variants of the mRNA

Question 13

You are interested in designing a molecular probe to detect the region of βˢ SNP,which includes a DdeI (CTNAG)restriction site.Which of the following molecular probe sequences would anneal to the correct position?

A)ACTCCTGAGGAGAAG
B)TGAGGACTCCTCTTC
C)GTGCACCTGACTCCT
D)CACGTGGACTGAGGA
E)CACGUGGACUGAGGA

Question 14

Thalassemia is a recessive blood disease caused by reduced synthesis of one of the globin genes.While SCD is a mutation in the structure of hemoglobin,thalassemias can also be caused by mutations in the regulatory elements,causing too little globin to be produced and resulting in anemia.You've designed a DNA probe that you want to use to screen a family for a rare mutation in the β-globin gene that causes thalassemia.First you will use the probe for northern blotting.What information will the northern blot tell you?

A)whether the mRNA for β-globin is being translated into functional proteins in a given cell population
B)whether the amount of the β-globin gene being transcribed (mRNA levels)is within normal range
C)the size of the mRNA being transcribed
D)the presence of a particular mutation by restriction fragment analysis
E)whether the amount of the β-globin gene transcript is within normal range,and the size of the mRNA gene product

Question 15

At a biological level,βᴬβˢ heterozygotes suffer fewer cases of malaria than βᴬβᴬ homozygotes,and when they do get malaria,their disease is less severe.What is the biological explanation for the heterozygous advantage?

A)The βᴬβᴬ homozygotes have a shortened average life span of their red blood cells,and the shorter RBC life spans interrupt the developmental cycle of Plasmodium larvae by causing the parasites to mature and reproduce rapidly.
B)The βᴬβˢ heterozygotes have a shortened average life span of their red blood cells,and the shorter RBC life spans interrupt the developmental cycle of Plasmodium larvae by preventing many of the immature parasites from reaching maturity.
C)The sickle-cell shape of the RBCs in βᴬβˢ heterozygotes causes the Plasmodium larvae to become stuck in the RBC aggregates and prevents reproduction.
D)The anemia associated with SCD makes the βᴬβˢ heterozygotes less attractive to mosquitoes,so they experience fewer mosquito bites and less opportunity for infection by Plasmodium larvae.
E)The βᴬβˢ heterozygotes are bitten by mosquitoes less frequently,and when they are infected,the sickle-cell shape of the RBCs in βᴬβˢ heterozygotes causes the Plasmodium larvae to become stuck in the RBC aggregates and prevents reproduction.

Question 16

How is the DNA visualized on a Southern blot?

A)ethidium bromide
B)radioactively labeled probes
C)chemically labeled probes
D)both ethidium bromide and chemically labeled probes
E)either radioactively labeled probes or chemically labeled probes

Question 17

You set up an EcoRI restriction digest for a sample of genomic DNA from an individual with a hemoglobin mutation.To your surprise,you notice a different pattern of bands in the affected individualyou have identified a new SNP! What can you conclude from the pattern of bands from the gel below?

A)The SNP resulted in the loss of an EcoRI site.
B)The SNP resulted in the creation of a new EcoRI site.
C)The SNP resulted in the loss of an exon.
D)The SNP results in the creation of a new HindIII site.
E)There was no change in the genomic DNA sequence.

Question 18

Hemoglobin,the protein responsible for binding and transporting oxygen,forms a tetramer.What is the protein composition of the most common form of hemoglobin,hemoglobin A (HbA)?

A)α₁β₁
B)α₁β₂
C)α₂β₁
D)α₂β₂
E)α₂βS

Question 19

Ingram examined hemoglobin structural variation by breaking down the hemoglobin protein into many fragments by chemical treatment and subjecting the fragments to electrophoresis to separate them in a gel;and then in a second dimension,perpendicular to the first,he separated them by chromatography.This two-step approach is commonly referred to as

A)hybridization.
B)electrophoretic mobility.
C)densitometry.
D)restriction fragment analysis.
E)peptide fingerprint analysis.

Question 20

Which of the following techniques quantifies the amount of protein present in a gel lane by measuring how much light is blocked from passing through the gel by the presence of a band of protein?

A)hybridization
B)electrophoretic mobility
C)densitometry
D)restriction fragment analysis
E)peptide fingerprint analysis

Question 21

The different globin genes in each cluster are sequentially expressed in tightly controlled patterns during the various stages of prenatal and adult development.What gene structure helps regulate globin gene transcription by controlling both the timing and the starting point for transcribing DNA into mRNA?

Question 22

A SNP results in a loss of the XhoI site indicated,so you design a molecular probe that spans the lost XhoI site.Which lane represents the expected Southern blot of an individual who is a carrier (heterozygous)for the mutant allele?

Question 23

Given the following Southern blot results,which lane represents a heterozygous individual?

Question 24

A couple has four children;one is affected by SCD,and two are carriers of the disease.What can be said of the genotypes of the parents?

Question 25

Given the following gel,which protein has a more negative charge?

Question 26

Hemoglobin is made up of four proteins from two different gene clusters,the α-globin gene cluster and the β-globin gene cluster.The two clusters are related,having evolved from a common ancestral gene through gene duplication,based on strong similarities in which three gene characteristics?

Question 27

The bone marrow must continuously generate new red blood cells because the life span of a typical red blood cell is only ________.The life span is even shorter in individuals with sickle-cell trait,which accounts for the protective effects against malaria.

Question 28

Given the following plasmid,what are the sizes of the fragments you would expect from a NotI digest?

Question 29

Sodium dodecyl sulfate (SDS)is a detergent commonly added to protein samples before gel electrophoresis.The purpose of the negatively charged SDS is to neutralize the charges and denature the protein to remove secondary structures.Thus,the proteins can be separated on a gel based solely on what?

Question 30

Given the following gel,which DNA fragment has a lower molecular mass?

Question 31

Based only on this Southern blot and with no knowledge of which of the β-globin SNPs you are looking at,which lane(s)might represent(s)a heterozygous individual?

Question 32

The rate of molecule movement in electrophoretic gels depends on three parameters of molecular structure.Each of these parameters individually is important in determining how a particular molecule migrates,but they can also interact with one another to produce a characteristic migration rate for each molecule.What are the three parameters?

Question 33

Which of the following images represents the expected results of a DNA gel for three individuals with different genotypeshomozygous dominant,heterozygote,and homozygous recessive?

Question 34

What information allows you to predict the pattern of DNA bands expected in a Southern blot of an individual with the wild-type allele?

Question 35

Given the following plasmid,what are the sizes of the fragments you would expect from an XhoI digest?

Question 36

As part of the maturation process,red blood cells lose their nucleus.What is the consequence for cell division in these cells?

Question 37

You have digested a molecule of DNA and want to identify a specific fragment of interest.The DNA is subjected to gel electrophoresis,but you get two bands that are very close in size.What could you use to determine which band is the correct one?

Question 38

Given the following gel,which DNA fragment has a lower electrophoretic mobility?

Question 39

Given the following gel,which protein is more likely to have a globular shape?

Question 40

Before transferring DNA from a gel to the membrane in Southern blotting,the DNA must be denatured (usually by soaking the gel in NaOH).Why is this step necessary?

Question 41

We saw that Southern blotting of DNA from the βᴬ allele produces two DNA bands corresponding to fragment lengths of 1150 bp and 200 bp based on the location of two DdeI sites.In contrast,Southern blot analysis of βˢ-allele DNA produces a single DNA restriction fragment,measuring 1350 bp in length,since one of the DdeI sites is altered by SNP variation.Why is Southern blotting necessary to identify the correct bandsif you know the sizes,why can't you just identify your band on a gel? Why is the location of the probe (spanning the predicted lost DdeI site)important?

Question 42

Burkitt's lymphoma is a cancer of the lymphatic system.The endemic variant,common to equatorial Africa,commonly affects children who are also affected by chronic malaria.A recent study found that individuals with AA hemoglobin were twice as likely to develop Burkitt's lymphoma as those with the AS genotype.We saw a similar benefit of certain genotypes in cases of sickle cell disease.Recall that individuals who are βᴬβˢ,βᴬβᶜ,or βᴬβᴱ have a survival and reproductive advantage over individuals who are homozygous βᴬβᴬ (and therefore succumb more easily to malaria)and over those who are homozygous for the mutant alleles (and therefore suffer from hereditary anemia).Resistance to malaria and Burkitt's lymphoma are both an example of ________ advantage.

Question 43

Being a carrier of the sickle cell trait,although generally not a serious problem,can pose significant risks for athletes,particularly those in intense training regimens.The death of Florida State University linebacker Devaughn Darling,a carrier of the sickle cell trait,in a spring conditioning drill refocused attention on sickle cell abnormalities,including both sickle cell disease and sickle cell trait (carriers).High altitude,aggressive exercise,and high temperatures can all lead to acute rhabdomyolysis in individuals with sickle cell trait.Why do you think an individual who is a carrier of the sickle cell trait may be more likely to experience the symptoms of SCD during rigorous exercise?

Question 44

Northern blotting is not useful in detecting the SNPs associated with the βᴬ and βˢ alleles.Explain why.

Question 45

Globin genes contain ________ segments that ultimately encode the amino acids of the protein and interspersed ________ sequences that do not contribute to encoding the protein product of the gene.

Question 46

The intercalating agent ________ allows researchers to visualize DNA and RNA on a gel when the gel is exposed to UV light.

Question 47

Describe the hypothesis that James Neel proposed to describe the inheritance pattern of SCD.What experimental methods did he use to prove his hypothesis?

Question 48

We can detect the SNP in the βˢ allele because it destroys a DdeI restriction site,leading to DNA restriction fragment variation revealed by Southern blot analysis.
Either two or three restriction sequences for the restriction endonuclease DdeI can occur near the β-globin gene,depending on the allele.One DdeI restriction sequence is eliminated from the βˢ allele by the SNP in the mutant allele because of a mutation in the double-stranded target sequence 5′ - CTNAG - 3′.
Suppose the wild-type allele sequence is CCTGAG,while a newly identified SNP is CCTTAG.Would this same restriction fragment analysis technique be appropriate for detecting this particular SNP? What other technique(s)could you use to identify this particular mutation?

Question 49

In contrast to the nucleic acid probes used to detect DNA or RNA target sequences,molecular probes used to detect target proteins in western blots are ________.