Why are regions between genes (intergenic regions) often chosen as mapping markers in genome-wide association studies? Please select all that apply.

A) Intergenic regions are usually not under positive or negative selection
B) Polymorphism frequency in intergenic regions is usually unaffected by the health of the individuals
C) Intergenic regions are less likely to contain crossovers during meiosis
D) Variation in intergenic regions is more strongly linked to ethnicity than is variation in genic regions