Abstract
The 1953 discovery of the DNA double-helical structure by James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin, represented one of the most significant advances in the biomedical world (Watson and Crick 1953; Maddox 2003). Almost half a century after this landmark event, in February 2001, the initial draft sequences of the human genome were published (Lander et al., 2001; Venter et al., 2001) and, in April 2003, the International Human Genome Sequencing Consortium reported the completion of the Human Genome Project, a massive international collaborative endeavor that started in 1990 and is thought to represent the most ambitious undertaking in the history of biology (Collins et al., 2003; Thangadurai, 2004; National Human Genome Research Institute). The Human Genome Project provided a plethora of genetic and genomic information that significantly changed our perspectives on biomedical and social sciences. The sequencing of the first human genome was a 13-year, 2.7-billion-dollar effort that relied on the automated Sanger (dideoxy or chain termination) method, which was developed in 1977, around the same time as the Maxam-Gilbert (chemical) sequencing, and subsequently became the most frequently used approach for several decades (Sanger et al., 1975; Maxam & Gilbert, 1977; Sanger et al., 1977). The new generations of DNA sequencing technologies, known as next-generation (second generation) and next-next-generation (third generation) sequencing, which started to be commercialized in 2005, enabled the cost-effective sequencing of large chromosomal regions during progressively shorter time frames, and opened the possibility for new applications, such as the sequencing of single-cell genomes (Service, 2006; Blow, 2008; Morozova and Marra, 2008; Metzker, 2010).
TopInter-Individual Genetic Variations
The Human Genome Project unveiled similarities and differences at the DNA level within and between populations. Most importantly, it revealed that two unrelated individuals are approximately 99.9% identical at the DNA level (Shastry, 2002; Feuk et al., 2006). A very interesting part of the genome revolves around the remaining 0.1%, which constitutes inter-individual differences. Several million such differences, which occur approximately once every 300-1000 base pairs, exist between two random genomes, and they became known as Single Nucleotide Polymorphisms (SNPs) (Brookes, 1999; Manolio et al., 2008). SNPs were linked to many medical conditions including diabetes, cancer, and asthma, and some of them increase, while others decrease the risk to develop a specific disease (Kaklamani et al., 2008; Ionita-Laza et al., 2009; Kilpivaara et al., 2009). To characterize genomic variations and provide a public database of common genome-wide sequence variants, the International HapMap Project was initiated in October 2002 (The International HapMap Consortium, 2003). Its second-generation map, published in 2007, reported over 3.1 million SNPs, and provided a valuable resource to study gene-disease interactions (The International HapMap Consortium, 2007).