Figure 1. Three major forms of genetic diversity. (a) Diversity at the level of single nucleotides. The individual is heterozygous for one nucleotide in this sequence having inherited a C from the father and a T from the mother. (b) Short tandem repeat polymorphisms exhibit varying numbers of short repeats, such as the CAGA sequence shown here. The individual has inherited eight CAGA repeats from the father and five from the mother. (c) Interspersed repeats are scattered in a single copy throughout the genome. In this case, the middle interspersed repeat is present on the paternal chromosome but absent on the maternal chromosome.

Figure 2. Comparison of genetic diversity at the nucleotide level in humans and chimpanzees. The nuclear DNA sequence consists of 10 154 bp of DNA from the X-chromosome, and the mitochondrial DNA consists of 320 bp of DNA. Data taken from Kaessmann H, Wiebe V and Pääbo S (1999) Extensive nuclear DNA sequence diversity among chimpanzees. Science 286: 1159–1162.

Figure 3. Illustration of the coalescent process. Although the ancestral population contains multiple individuals, all lineages but one eventually become extinct. Thus, all of the variation in the current population can ultimately be traced to one common ancestor.

Figure 4. Tree diagram illustrating the genetic distances among 22 human populations. Genetic distances were estimated using 100 Alu insertion polymorphisms (Watkins WS, Rogers AR, Ostler CT et al. (2003) Genetic variation among world populations: inferences from 100 Alu insertion polymorphisms. Genome Research 13: 1607–1618).

Figure 5. Tree diagram illustrating the genetic distances between 15 human populations, using 11 078 SNPs to estimate genetic distances. Data from Shriver MD, Mei R, Parra EJ et al. (2005) Large-scale SNP analysis reveals clustered and continuous patterns of human genetic variation. Human Genomics 2(2): 81–89.