Genetic Similarities: Wilson, Sarich, Sibley, & Ahlquist (2 of 3)

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Testing Similarity Using DNA
Scientists studying the chemistry of DNA moved even closer to actual sequences. Charles Sibley (left) and Jon Ahlquist pioneered the use of DNA kinetics to investigate evolutionary relationships using a technique called DNA-DNA hybridization (see figure, right). Each DNA molecule is made of two strands of nucleotides. If the strands are heated, they will separate—and as they cool, the attraction of the nucleotides will make them bond back together again. To compare different species, scientists cut the DNA of the species into small segments, separate the strands, and mix the DNA together. When the two species’ DNA bonds together, the match between the two strands will not be perfect since there are genetic differences between the species—and the more imperfect the match, the weaker the bond between the two strands. These weak bonds can be broken with just a little heat, while closer matches require more heat to separate the strands again.

DNA hybridization can measure how similar the DNA of different species is—more similar DNA hybrids “melt” at higher temperatures. When this technique was applied to primate relationships, it suggested that humans and chimpanzees carried DNA more similar to one another’s than to orangutans’ or gorillas’ DNA.

Hypothesized evolutionary relationships between humans and their close relatives based on DNA-DNA hybridization data.

• Sibley image courtesy of Thayer Birding Software.