The genetic material of most living organisms is DNA. Undoubtedly, the Human Genome Project, announced in 2001, has remained in everyone's mind after countless studies carried out for centuries to determine the structure of DNA, to determine the differences between living things, and to reveal the effects of environmental factors on our genetics. Although the statement made in 2001 sounds like the beginning of the process, it actually dates back to the establishment of the Human Genome National Study Center in the USA in 1989. We have learned a lot from the data obtained from this project so far. One of the most important of these information is that the sequence similarity of the genomes of two people is 99.99%, and the other is that there are 1.4 million single nucleotide polymorphisms (SNPs, single nucleotide polymorphisms) in the human genome. Although it was expected that all questions would be answered at that time with the data obtained from the research, we can say that everything actually started at that time and therefore it is a project that we can consider as a milestone for genome research. Thus, the relationships between human genomic variation and the risk of developing diseases have begun to be examined. The importance of identifying gene variants such as SNPs, which we call single nucleotide polymorphisms that we can express in the order of hundreds, and variants depending on copy numbers in understanding the complex structures of diseases, has greatly contributed to the formation of today's information. The phenotype of the individual differs according to the genetic (genotype) and the external appearance of the features created by environmental factors) according to the variants of the genes and the environmental effect. We also know that each person carries approximately 4 million genetic variants, and most of these variants do not contribute to phenotypic diversity or disease risk and reach significant proportions by chance in populations. The fact that the SNPs we mentioned above constitute the largest class of genetic variation among humans will lead to the identification and characterization of these SNPs, and to become the most important data to be used by personal medicine in the not too distant future. Establishing the relationship of these differences with nutrition and diseases started the age of precision medicine after the Human Genome Project.