Sources suitable for PCR: from which sample types can a specific DNA fragment be amplified?

Introduction / Context:
Polymerase chain reaction (PCR) revolutionized molecular biology and forensics by enabling exponential amplification of target DNA sequences from minute biological samples.

Given Data / Assumptions:

• All listed tissues (blood, hair follicle, skin) contain nucleated cells with genomic DNA.
• Even small amounts of DNA are sufficient for PCR after extraction.
• PCR requires primers flanking the target sequence, thermostable polymerase, dNTPs, and cycling.

Concept / Approach:
If a sample contains intact DNA molecules, PCR can amplify a chosen fragment. Drops of blood (white cells), hair follicles (root sheath cells), and skin fragments all provide DNA templates. Thus, each source is acceptable, making “All of these” correct.

Step-by-Step Solution:
Extract DNA from the chosen biological material.Design primers bracketing the target locus.Run thermal cycles: denaturation, annealing, extension.Analyze amplicons by gel electrophoresis or sequence as needed.

Verification / Alternative check:
Quantitative PCR and control amplifications verify template integrity; negative controls exclude contamination.

Why Other Options Are Wrong:

• Each individual sample type is valid; choosing any single one ignores the others' validity.
• None of these: Incorrect because all provide usable DNA.

Common Pitfalls:
Confusing hair shaft (often low/fragmented DNA) with hair follicle (good DNA source). The option explicitly names the follicle.

Final Answer:
All of these.