Genetic mapping basics — Which statement is correct with respect to locating genetic traits using molecular tools such as restriction enzymes and markers?
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AKnown protein-coding sequences are too far apart to allow linkage determination for most new genes
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BRestriction sites allow DNA molecules to be cut (digested), enabling mapping and marker analysis
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CEvery protein-coding gene is always associated with a unique restriction pattern
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DNone of the above statements is correct
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ELinkage mapping does not use DNA markers at all
Answer
Correct Answer: Restriction sites allow DNA molecules to be cut (digested), enabling mapping and marker analysis
Explanation
Introduction:Locating the chromosomal position of a trait can rely on molecular techniques that convert DNA sequence differences into visible markers. This question checks your understanding of how restriction enzymes and related markers contribute to genetic mapping and trait localization.
Given Data / Assumptions:
- Restriction endonucleases recognize specific short DNA sequences and cut at or near those sites.
- Polymorphisms that create or abolish sites underlie RFLP markers.
- Linkage analysis tracks co-segregation of markers and phenotypes within pedigrees or populations.
Concept / Approach:The core enabling step is cutting DNA at defined sequences to generate fragments that can be separated and compared. Differences in fragment sizes reflect polymorphisms useful for linkage to traits. While not every gene presents a convenient pattern, restriction digestion is foundational for constructing maps and markers (alongside VNTRs, SNPs, and microsatellites).
Step-by-Step Solution:
1) Use restriction enzymes to digest genomic DNA or PCR products at known sites.2) Separate fragments (e.g., gel electrophoresis) to observe size differences caused by polymorphisms.3) Associate marker alleles with the trait through linkage or association studies.4) Refine location using additional markers and recombination data.Verification / Alternative check:Classic RFLP maps and newer SNP arrays both exploit sequence-defined landmarks; restriction digestion pioneered the approach and still underpins many genotyping workflows (e.g., CAPS markers in plants).
Why Other Options Are Wrong:
a) Linkage is feasible because markers are dense; the statement is unjustified.c) Not every coding gene has a unique restriction pattern detectable in a given assay.d,e) Both contradict the well-established role of DNA markers and restriction mapping.Common Pitfalls:Assuming mapping requires protein assays; modern mapping predominantly uses DNA-level polymorphisms, not protein patterns.
Final Answer:Restriction sites enable DNA digestion, which supports mapping via molecular markers.