Y-SNP allele frequencies differ markedly between continental populations to predict paternal origin. Haplogroups correlate strongly with physical appearance in pale-skinned Caucasians, dark-skinned Caucasians, Africans/Caribbeans, South Asians, East Asians, Middle Easterners. Frequencies differ significantly between six ethnic appearance groups. Ancient Y-SNP mutations define clades A-R tied to continents of origin. Stronger geographic association than mtDNA due to male reproductive variance and patrilocality. Signet Y-SNP kit yields reliable results from 1 ng DNA in blood, saliva, post-coital swabs. Highly male-specific with reliable results despite 1000-fold excess female DNA. No erroneous calls in degradation studies despite locus loss. Few artifacts in primates but incompatible with human phylogeny. Superior to STRs for ancestry inference in forensics. Haplogroups reflect progressive Y-lineage diversification without recombination. Subclades show localized distributions from recent migrations. Enables prioritization of forensic enquiries by predicted appearance. Samples from 627 UK individuals across ethnic groups confirm correlations. Kit uses Luminex 100 for reproducible haplotyping in two multiplexes.