The invention provides improved methods, compositions, and kits for detecting ploidy of chromosome regions, e.g. for detecting cancer or a chromosomal abnormality in a gestating fetus. The methods can utilize a set of more than 200 SNPs that are found within haploblocks and can include analyzing a series of target chromosomal regions related to cancer or a chromosomal abnormality in a gestating fetus. Finally the method may use knowledge about chromosome crossover locations or a best fit algorithm for the analysis. The compositions may comprise more than 200 primers located within haplotype blocks known to show CNV.