Q.26 A genetic linkage map represents the
(A) relative locations of genes on a chromosome
(B) distribution of the mutational hotspots
(C) phylogenetic linkage among organisms
(D) accurate physical distances among loci
A genetic linkage map represents the relative locations of genes on a chromosome, making option (A) the correct answer for this CSIR NET Life Sciences question.
Option Analysis
Genetic linkage maps rely on recombination frequencies during meiosis to order genes, not physical measurements. Option (A) matches this definition precisely, as maps show gene positions relative to each other based on crossover rates measured in centimorgans (cM). Option (B) refers to mutational hotspots, which physical maps or mutation rate studies identify, not linkage maps. Option (C) describes phylogenetic trees for evolutionary relationships among species, unrelated to chromosomal gene positioning. Option (D) implies precise base-pair distances, which physical maps provide via sequencing, whereas linkage maps approximate positions indirectly.
Introduction: Unlocking Genetic Linkage Map and Relative Locations of Genes on Chromosome
In genetics, a genetic linkage map visualizes the relative locations of genes on a chromosome using recombination data from meiosis. This tool, essential for CSIR NET Life Sciences, helps map gene order without measuring exact DNA distances.
Core Concept
Linkage maps plot genes based on crossover frequency: closer genes recombine less (low cM), while distant ones recombine more. Developed by Alfred Sturtevant, they form linkage groups matching chromosomes in model organisms like Drosophila.
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Recombination frequency = map distance in centimorgans (1 cM = 1% recombination).
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Used in QTL mapping, breeding, and disease gene hunts.
Versus Physical Maps
| Feature | Genetic Linkage Map | Physical Map |
|---|---|---|
| Basis | Recombination frequency | DNA sequence/base pairs |
| Distance | Relative (cM) | Accurate (bp/Mb) |
| Resolution | Coarse (~1 Mb) | Fine (precise loci) |
| Application | Gene order, inheritance | Sequencing, cloning |
Physical maps offer accurate physical distances among loci, distinguishing them from linkage maps.
CSIR NET Relevance
Questions like “A genetic linkage map represents the” test understanding of relative locations of genes on a chromosome over distractors like mutational hotspots or phylogeny. Practice with testcross data to calculate RF and build maps.
