I am reading some articles on genetic variations and I see there are two types of analysis one is genome wide genetic variation analysis and second one is locus specific genetic variation analysis. I don't understand what these two, genome wide and locus specific analysis mean and what is the difference between these two analysis or why do we need both type of analysis?
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A locus (plur. loci) is a region of arbitrary size on a chromosome. A locus can be a single nucleotide or it can much larger (like $10^7$ sites).
A genome-wide analysis is therefore an analysis using the whole genome at once while a locus-specific analysis is the same analysis performed at the level of individual loci.
To make an analogy, if a genome-wide analysis is like a country-wide analysis, then a locus specific analysis is like a city specific analysis.
Without more context, it will not be possible to say more than that!