Question

Which molecular technique is used to identify genetic variants in human DNA?

• A. PCR-RFLP
• B. FISH
• C. Karyotyping
• D. Chromosomal banding

Hint:

Distinguish between techniques for gene-level analysis and chromosome-level analysis. PCR-based methods like PCR-RFLP and sequencing are used for small-scale genetic variants (genes, SNPs). Karyotyping, banding, and FISH are used for large-scale chromosomal abnormalities.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Genetic variants are differences in DNA sequences among individuals. These can range from single nucleotide changes (SNPs) to larger structural changes in chromosomes. Different molecular techniques are designed to detect different types of variations.
Step 2: Detailed Explanation:
Let's analyze the techniques:
- PCR-RFLP (Polymerase Chain Reaction - Restriction Fragment Length Polymorphism): This is a technique used to identify variations in DNA sequences at a specific location. It involves amplifying a DNA region with PCR and then cutting the amplified product with a restriction enzyme. If a genetic variant alters the recognition site for the enzyme, the resulting fragments will be of a different length. This difference in fragment length (polymorphism) allows for the identification of the genetic variant. It is specifically designed to detect small-scale variations like SNPs.
- FISH (Fluorescence In Situ Hybridization): This technique uses fluorescent probes that bind to specific parts of a chromosome. It is used to visualize and map genetic material, and can detect large-scale changes like chromosomal aneuploidy (abnormal number of chromosomes) or large deletions/translocations, but not small genetic variants like SNPs.
- Karyotyping: This is a laboratory procedure that produces an image of an individual's chromosomes. It is used to look for abnormalities in chromosome number (e.g., Down syndrome, which has an extra chromosome 21) or large-scale structural changes. It cannot detect small genetic variants within a gene.
- Chromosomal banding: This is a technique used in conjunction with karyotyping. It involves staining chromosomes to produce a characteristic pattern of light and dark bands. It helps in identifying chromosomes and detecting large structural abnormalities, but its resolution is too low to identify variants at the DNA sequence level.
Step 3: Final Answer:
Among the given options, PCR-RFLP is the technique specifically designed to identify small genetic variants, such as single nucleotide polymorphisms (SNPs), in a targeted DNA sequence. The other techniques are used for analyzing chromosomes at a much larger, structural level.