Encyclopedia of Clinical Neuropsychology

2011 Edition
| Editors: Jeffrey S. Kreutzer, John DeLuca, Bruce Caplan


  • John DeLuca
Reference work entry
DOI: https://doi.org/10.1007/978-0-387-79948-3_1855


Allele is an alternate form of a gene, which is the basic unit of inheritance. A gene is located at a particular site on the chromosome, and can have several alleles for that locus. For example, A, B, and O are different alleles for the ABO blood-type marker locus of a gene. Alleles greatly influence the expression of physical and behavioral phenotypes or traits such as eye color. For instance, the apolipoprotein E (APoE) gene is a well-known risk factor for developing Alzheimer’s disease. The APoE gene has three common alleles: epsilon 2, epsilon 3, and epsilon 4. There is some evidence that carriers of the APoE epsilon 4 allele are at a greater risk for the development of Alzheimer’s disease. In contrast, the APoE epsilon 3 allele has been suggested as a “protective” factor in the development of Alzheimer’s disease (Plomin, Defries, Craig, & McGuffin, 2003).

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References and Readings

  1. Plomin, R., Defries, J. C., Craig, W., & McGuffin, P. (2003). Behavioral genetics in the postgenomic era. Washington, DC: American Psychological Association.Google Scholar

Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  • John DeLuca
    • 1
  1. 1.Neuropsychology and Neuroscience LaboratoryKessler Foundation Research CenterWest OrangeUSA