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Definition of Dominant

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Dominant: A genetic trait is considered dominant if it is expressed in a person who has only one copy of that gene. (In genetic terms, a dominant trait is one that is phenotypically expressed in heterozygotes).

A dominant trait is opposed to a recessive trait which is expressed only when two copies of the gene are present. (In genetic terms, a recessive trait is one that is phenotypically expressed only in homozygotes).

Examples of dominant disorders include:

  • Achondroplasia (a common form of dwarfism with short arms and legs),
  • Familial hypercholesterolemia (high blood cholesterol leading to premature coronary artery disease),
  • Huntington disease (a form of progressive dementia from which the folk singer Woody Guthrie suffered),
  • Neurofibromatosis (NF1)(a neurologic disorder with an increased risk of malignant tumors), and
  • Polycystic kidney disease (of adult onset).

Most dominant traits are due to genes located on the autosomes (the non-sex chromosomes). An autosomal dominant trait typically affects males and females with equal likelihood and with similar severity. The gene responsible for it can be transmitted from generation to generation and each child born to someone with the gene has a 50:50 chance of receiving the gene and manifesting the disease.

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Reviewed on 12/4/2018

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