Noun
isochromosome (plural isochromosomes)
(cytology) An abnormal chromosome in which one arm has been lost and replaced with an exact copy of the other arm.
Meiotic errors that lead to the production of X with p arm deletions or abnormal Y chromosomes are also mostly found in the father. citation Isochromosome X or ring chromosome X on the other hand are formed equally often by both parents. Source: Internet