Genome mapping — A chromosome map that uses cloned and sequenced DNA fragments (e.g., restriction fragments, contigs, sequence-tagged sites) rather than classical genetic markers is known as what?
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AA physical map
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BA genetic map
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CA cloning map
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DNone of these
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EAn epigenetic map
Answer
Correct Answer: A physical map
Explanation
Introduction / Context:Genome maps come in multiple types. Genetic (linkage) maps order markers based on recombination frequencies in crosses. Physical maps place DNA features according to actual base-pair distances along chromosomes using molecular tools such as restriction mapping, BAC contigs, and sequence assemblies. Understanding the distinction is vital for positional cloning and genome assembly.
Given Data / Assumptions:
- Question emphasizes cloned and sequenced DNA fragments.
- Focus is on absolute order and distances in base pairs, not recombination frequency.
- Terminology follows standard genomics usage.
Concept / Approach:A physical map represents the literal arrangement of DNA sequences. Early physical maps used restriction fragment maps and overlapping clone contigs; modern approaches rely on long-read sequencing and scaffolding to create near-complete assemblies. Genetic maps complement physical maps but can differ due to recombination hot/cold spots.
Step-by-Step Solution:
Identify the map type that uses cloned/sequenced fragments → physical map.Differentiate from genetic map (recombination-based).Exclude vague or nonstandard terms like “cloning map.”Verification / Alternative check:Human genome project milestones included both a high-resolution physical map of BAC contigs and genetic linkage maps; both were necessary but distinct.
Why Other Options Are Wrong:
b) Genetic maps use centiMorgan distances based on recombination, not cloned fragment positions.c) “Cloning map” is not a standard map category in genomics.d) A correct option exists.e) Epigenetic maps profile chromatin marks or methylation, not cloned fragment positions.Common Pitfalls:Assuming higher recombination frequency equals larger physical distance; recombination landscapes vary significantly across genomes.
Final Answer:A physical map.