Definition of overdominance in US English:

overdominance

noun

  • 1Excessive dominance.

  • 2Genetics. A condition in which a heterozygote (having a copy of two different alleles of a gene) has a phenotype which falls beyond the extremes of the range represented by the corresponding homozygotes (having two copies of one or other of the alleles).

Origin

Early 20th century. From over- + dominance.

Pronunciation

overdominance

/ˌəʊvəˈdɒmɪnəns/