1.2 Genes influence susceptibility to many diseases and disorders. (a) An X-ray of the hand of a person suffering from diastrophic dysplasia (bottom), a hereditary growth disorder that results in curved bones, short limbs, and hand deformities, compared with an X-ray of a normal hand (top). (b) This disorder is due to a defect in the SLC26A2 gene on chromosome 5.

[Part a: (top) Biophoto Associates/Science Source; (bottom) Reprinted from Johanna Hästbacka et al., The diastrophic dysplasia gene encodes a novel sulfate transporter: Positional cloning by fine structure linkage disequilibrium MAPping. Cell 78(6):1073–1087, 1994. © 1994 Elsevier. Courtesy of Prof. Eric Lander, Whitehead Institute, MIT.]