The Importance of Human Genetic Variation
Source: http://nutrigenomics.ucdavis.edu/geneticvariation.htm

Thanks to human genomic research, we now know that all people share the vast majority of human genetic information. Indeed, any two individuals share 99.9% of their DNA sequence - or about 1 difference in every 1000 base pairs. Many of the sequence variations are single nucleotide polymorphisms (SNPs) and SNPs individually or as groups alter regulation of gene expression, mRNA processing (splicing, half-life, etc), and protein and enzyme activities. Hence, each individual may have unique responses to environmental factors based upon the distinctive combination of SNPs in their genomic DNA.

Similarly, all racial and ethnic groups share most genetic variation. The small differences that do exist are responsible for human diversity such as hair and skin colors, height and weight potential, and all other "gene-based" variation. Some of these small differences also involve many medically important variations including susceptibility to disease. Therefore, while much of human genetics research will apply broadly to all groups of people, regardless of the individuals studied, it is also important to analyze the genetic differences that may underlie disparate rates in the incidence or patterns of progression among different groups. Risk factors for common diseases such as obesity, coronary heart disease, diabetes, prostate cancer, and birth defects must take into account both genetic and environmental/behavioral/social factors. The science of nutrigenomics takes a multi-disciplinary and multi-dimensional approach to understanding how genes, diet, and disease interact to create health disparities for certain human populations that evolved from different geographic regions.