The global family. A network illustrating the relatedness of a series of DNA sequences within a 10,000-base pair segment of the human X chromosome sampled from 70 individuals worldwide. Identical DNA sequences found in people living on three different continents are illustrated by circles containing three faces; identical DNA sequences found in individuals from two continents are depicted as circles containing two faces; sequences that are found only among individuals inhabiting one continent are depicted as circles containing one face. A DNA sequence that is ancestral to all of the other sequences (arrow) is found in individuals from all continents. Black dots on the lines connecting the circles denote nucleotide substitutions in the DNA sequences. The network demonstrates that people from different continents often carry identical DNA sequences. Consequently, how a person looks gives little or no clue to what alleles he or she may carry at any particular locus. [Modified from (6)]
