Efforts to identify the origins of Ashkenazi Jews through DNA analysis began in the 1990s. Like most DNA studies of human migration patterns, the earliest studies focused on two segments of the human genome, the Y-chromosome (passed on only by males), and the mitochondrial genome (mtDNA, passed on only by females). Both segments are unaffected by recombination. Genome-wide association studies have also been employed to yield findings relevant to genetic origins. Genetic studies revealed that Ashkenazi Jews originated in Middle East during Bronze Age (between 2500 BC and 700 BC) spreading later to Europe.[60]