| hitchhiker | A gene that has no selective advantage, or may even be harmful, but that nevertheless temporarily becomes widespread because it is closely linked and coupled with a highly advantageous gene that is strongly selected. (05 Mar 2000) |
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| hitchhiker thumbs | Malposition of the thumb's which as a result of shortness of the first metacarpal stand at right angles to the radial border of the hand and in the same place as it; a characteristic sign of diastrophic dwarfism. (05 Mar 2000) |