A gene occupies a fixed position (locus) on a particular DNA molecule
Every gene sits at a precise, unchanging location on a chromosome. Biologists call this fixed address the gene's locus.
Real World
The BRCA1 gene always occupies locus 17q21 on chromosome 17; this fixed address allows genetic testing companies like 23andMe to reliably screen thousands of customers for cancer-risk mutations.
Exam Focus
Distinguish 'locus' (position on chromosome) from 'allele' (version of the gene) — confusing them is a common dropped mark.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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