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Choose the answer that is most appropriate for each question.
4.1. HindIII is a restriction endonuclease. Which of the following sequences is most likely to be recognized by this enzyme?
A. AAGAAG
B. AAGAGA
C. AAGCTT
D. AAGGAA
E. AAGTTC
Correct answer = C. The majority of restriction endonucleases recognize palindromic sequences in double-stranded DNA, and AAGCTT is the only palindrome among the options. Since only one DNA strand is provided, the complementary strand's base sequence must be determined. To be a palindrome, both strands must have the same sequence when read in the 5′→3′ direction. Therefore, the complement of 5′-AAGCTT-3′ is also 5′-AAGCTT-3′.
4.2. A couple of Ashkenazi Jewish descent brings their 6-month-old son to the doctor with symptoms of listlessness, poor head control, and a fixed gaze. After evaluation, the child is diagnosed with Tay-Sachs disease, an autosomal-recessive disorder affecting lipid degradation. The couple also has a daughter. The family's pedigree is shown on the right, along with Southern blots of a restriction fragment length polymorphism closely linked to the gene for hexosaminidase A, which is defective in Tay-Sachs disease. Which statement regarding the daughter is most accurate?
A. She has a 25% chance of having Tay-Sachs disease.
B. She has a 50% chance of having Tay-Sachs disease.
C. She has Tay-Sachs disease.
D. She is a carrier for Tay-Sachs disease.
E. She is homozygous normal.
Correct answer = E. Since they have an affected son, both the biological father and mother must be carriers of Tay-Sachs disease. The affected son must have inherited a mutated allele from each parent. Based on the Southern blots, the mutant allele for this disease is linked to the 3-kilobase (kb) band, while the normal allele is linked to the 4-kb band. As the daughter only inherited the 4-kb band, she must be homozygous normal for the hexosaminidase A gene.
4.3. A physician wants to determine the global patterns of gene expression in two different types of tumor cells to develop personalized chemotherapy for each patient. Which technique would be most suitable for this purpose?
A. Enzyme-linked immunosorbent assay
B. Microarray
C. Northern blot
D. Southern blot
E. Western blot
Correct answer = B. Microarray analysis enables the simultaneous determination of mRNA production (gene expression) from thousands of genes. In contrast, a northern blot only measures mRNA production from one gene at a time. Western blots and enzyme-linked immunosorbent assays measure protein production (also gene expression) but only for one gene at a time. Southern blots are used for DNA analysis rather than the products of DNA expression.
4.4. A 2-week-old infant is diagnosed with a urea cycle defect. Enzyme analysis reveals no activity for ornithine transcarbamoylase (OTC), an enzyme involved in the cycle. Molecular analysis indicates that the messenger RNA (mRNA) product of the OTC gene is identical to that of a control. Which technique was most likely used to analyze mRNA?
A. Dideoxy chain termination
B. Northern blot
C. Polymerase chain reaction
D. Southern blot
E. Western blot
Correct answer = B. A northern blot allows the analysis of expressed messenger RNA (mRNA) in a specific cell or tissue. Southern blot is used for DNA analysis, while western blot is used for protein analysis. Dideoxy chain termination is used for DNA sequencing, and polymerase chain reaction is employed to generate multiple copies of a DNA sequence in vitro.
4.5. For the patient mentioned in the previous question, which phase of the central dogma was most likely affected? 

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Choose the ONE best answer.
4.1. HindIII is a restriction endonuclease. Which of the following is most likely to be the recognition sequence for this enzyme?
A. AAGAAG
B. AAGAGA
C. AAGCTT
D. AAGGAA
E. AAGTTC
Correct answer = C. The vast majority of restriction endonucleases recognize palindromes in double-stranded DNA, and AAGCTT is the only palindrome among the choices. Because the sequence of only one DNA strand is given, the base sequence of the complementary strand must be determined. To be a palindrome, both strands must have the same sequence when read in the 5′→3′ direction. Thus, the complement of 5′-AAGCTT-3′ is also 5′-AAGCTT-3′.
4.2. An Ashkenazi Jewish couple has their 6-month-old son evaluated for listlessness, poor head control, and a fixed gaze. Tay-Sachs disease, an autosomal-recessive disease of lipid degradation, is diagnosed. The couple also has a daughter. The family’s pedigree is shown to the right, along with Southern blots of a restriction fragment length polymorphism very closely linked to the gene for hexosaminidase A, which is defective in Tay-Sachs disease. Which of the statements below is most accurate with respect to the daughter?
A. She has a 25% chance of having Tay-Sachs disease.
B. She has a 50% chance of having Tay-Sachs disease.
C. She has Tay-Sachs disease.
D. She is a carrier for Tay-Sachs disease.
E. She is homozygous normal.
Correct answer = E. Because they have an affected son, both the biological father and mother must be carriers for this disease. The affected son must have inherited a mutant allele from each parent. Because he shows only the 3kilobase (kb) band on the Southern blot, the mutant allele for this disease must be linked to the 3-kb band. The normal allele must be linked to the 4-kb band, and because the daughter inherited only the 4-kb band, she must be homozygous normal for the hexosaminidase A gene.
4.3. A physician would like to determine the global patterns of gene expression in two different types of tumor cells in order to develop the most appropriate form of chemotherapy for each patient. Which of the following techniques would be most appropriate for this purpose?
A. Enzyme-linked immunosorbent assay
B. Microarray
C. Northern blot
D. Southern blot
E. Western blot
Correct answer = B. Microarray analysis allows the determination of messenger RNA (mRNA) production (gene expression) from thousands of genes at once. A northern blot only measures mRNA production from one gene at a time. Western blots and enzyme-linked immunosorbent assay measure protein production (also gene expression) but only from one gene at a time. Southern blots are used to analyze DNA, not the products of DNA expression.
4.4. A 2-week-old infant is diagnosed with a urea cycle defect. Enzymic analysis showed no activity for ornithine transcarbamoylase (OTC), an enzyme of the cycle. Molecular analysis revealed that the messenger RNA (mRNA) product of the gene for OTC was identical to that of a control. Which of the techniques listed below was most likely used to analyze mRNA?
A. Dideoxy chain termination
B. Northern blot
C. Polymerase chain reaction
D. Southern blot
E. Western blot
Correct answer = B. Northern blot allows analysis of the messenger RNA present (expressed) in a particular cell or tissue. Southern blot is used for DNA analysis, whereas western blot is used for protein analysis. Dideoxy chain termination is used to sequence DNA. Polymerase chain reaction is used to generate multiple, identical copies of a DNA sequence in vitro.
4.5. For the patient above, which phase of the central dogma was most likely affected?