The purpose of this protocol, based on the hypothesis that human hand-use preference (handedness) is largely dependent on the action of a single locus, is to collect samples allowing us to map a "handedness gene" via detection of linkage to any of eight potential candidate genes/regions or via a whole or partial genome scan. We calculate that a full 300 marker genome scan of 100 parents and sibling pairs (allowing linkage analysis at 10 cM resolution), or the equivalent amount of data from partial scans of 300 families, has a high likelihood of allowing us to map the proposed gene. Eligible families, consisting of pairs of left-handed siblings plus at least one right-handed parent, were identified during Phase I of this study in 1996-1998, with approval from the now-lapsed FCRDC IRB. In Phase II of this study, we have collected cheek swab samples for DNA isolation from members of 100 eligible families for use in the mapping studies. DNA samples will not be linked back to individuals but grouped under a random family code that links to a database with limited information, including hand use preference and family structure. In the next phase, we wish to map the locus from cheek swab samples we have on hand.