Locus: The Locus class
In selectSNPs: Optimal Selection of SNPs Using a Unified Local Function

This is a S4 Locus classs for a marker (e.g., SNP) locus.

This Locus class abstracts the information for a marker or SNP locus. It consists of six slots, as follows.

Name:: A character string as the name of this marker locus.
Chromosome:: A character string as the name of the chromosome for this marker.
Position:: A numeric number as the chromosomal position of this marker.
Maf:: A numeric number for the minor allele frquency at this locus.
Type:: A character specifying the type of this locus, which can be "A", "B", or "C". The default value is "C" when the input is missing.
Status:: A integer specifying the status of tihs locus, wihch can be 1 for obligatory markers or 0 otherwise. The default value is 0 when missing the input.