Which of the following types of information are needed to construct a karyotype?
I. Size of the chromosomes
II. Gene mutations of the chromosomes
III. Age of the individual
A. I only
B. II only
C. I and II only
D. I, II and III
Answer/Explanation
Answer: A. I only
Explanation:
- A karyotype is an image or chart of all the chromosomes in a cell, arranged by size, banding pattern, and centromere position. It is used to detect chromosomal abnormalities, such as extra or missing chromosomes (e.g., Down syndrome – trisomy 21).
- The size of the chromosomes is crucial for correctly pairing and ordering them in a karyotype.
- Gene mutations (changes in DNA sequence) are too small to be seen in a karyotype; they require molecular testing.
- The age of the individual is not required to construct a karyotype, although it may help interpret certain findings.
Answer Evaluation:
I. Correct – Chromosome size is essential for creating a karyotype.
II. Incorrect – Gene mutations are not visible in karyotypes; they require genetic sequencing.
III. Incorrect – Age is not needed to construct a karyotype, though it may aid diagnosis.
Which process is used in polymerase chain reaction (PCR)?
A. Transcription
B. Translation
C. Replication
D. Mutation
Answer/Explanation
Answer: C. Replication
Explanation:
- The polymerase chain reaction (PCR) is a laboratory technique used to make many copies of a specific DNA sequence, which is essentially a form of DNA replication done artificially in a test tube.
- PCR uses cycles of heating and cooling to separate DNA strands (denaturation), bind short primers (annealing), and build new DNA strands using Taq polymerase (extension).
- Transcription is the process of making RNA from DNA, and translation is making proteins from RNA. Mutation refers to changes in the DNA sequence—not copying it.
Answer Evaluation:
A. Incorrect – Transcription is copying DNA into RNA, not used in PCR.
B. Incorrect – Translation involves protein synthesis, not DNA amplification.
C. Correct – PCR is an artificial replication of DNA.
D. Incorrect – Mutation is a change in DNA, not a process used in PCR.
The flow chart summarizes methods of gene transfer.
Which enzymes are used in steps I and II?
Answer/Explanation
Answer: B
Explanation:
Step I: Cutting the plasmid and the human gene
- This involves cutting both the bacterial plasmid and the human gene of interest (e.g., insulin gene from pancreatic cells).
- The enzyme responsible for cutting DNA at specific sequences is a restriction enzyme (also called restriction endonuclease).
Enzyme used in Step I: Restriction enzyme
Step II: Joining the human gene with the plasmid
- This involves inserting the gene into the plasmid to form recombinant DNA.
- The enzyme that joins DNA fragments together is DNA ligase.
Enzyme used in Step II: DNA ligase
Question
A strand of DNA containing four codons with base sequence ACT GTA CTC TAC mutates, changing the base sequence to ACT ATG CTC TAC. What type of mutation has occurred?
A. Insertion
B. Substitution
C. Deletion
D. Degeneracy
▶️Answer/Explanation
Answer: B. Substitution
Explanation:
- A substitution mutation involves changing one base in the DNA sequence.
- In this case, the second codon changed from GTA to ATG, indicating that one base was substituted.
- The total length of the DNA strand remains the same, and no frameshift occurred.
Answer Evaluation:
A. Incorrect – Insertion adds a base, but the number of bases is unchanged.
B. Correct – A single base has been substituted, changing one codon.
C. Incorrect – Deletion removes a base, which is not the case here.
D. Incorrect – Degeneracy refers to multiple codons coding for the same amino acid; not a mutation type.