What is a genomic library? Genomic libraries used in molecular genetics are constructed from which source material?

Introduction / Context:
A genomic library is a collection of DNA clones that together represent the entire genome (or a large fraction) of an organism. It is fundamental for gene discovery and mapping.

Given Data / Assumptions:

• DNA is fragmented and inserted into vectors (e.g., BACs, cosmids, plasmids).
• Coverage aims to include coding and noncoding regions.
• Selection markers and hosts allow maintenance and screening.

Concept / Approach:
Genomic libraries are made from genomic DNA (nuclear and, if desired, organellar). In contrast, cDNA libraries, made from mRNA via reverse transcription, represent expressed genes only.

Step-by-Step Solution:
Isolate high-quality genomic DNA.Fragment DNA by partial digestion or shearing to a desired size range.Ligate into appropriate vectors and transform.Screen clones by hybridization or PCR.

Verification / Alternative check:
Library complexity and insert size distribution can be assessed by colony PCR and restriction mapping; coverage calculated from genome size and clone number.

Why Other Options Are Wrong:
RNA and mRNA are not used directly for genomic libraries; cDNA reflects transcripts, not the whole genome; restricting to mitochondrial DNA excludes nuclear content.

Common Pitfalls:
Confusing genomic vs cDNA libraries; underestimating coverage needed for complete representation.

Final Answer:
Genomic DNA of an organism.