has_extent lost aneusomic chromosome 0 absent aneusomic chromosome This 'lost' chromosome is conceptually a 'deletion' in a genome that received zero copies of a chromosome in a cell division following a non-disjunction event. As such, it qualifies as a type of sequence_alteration. But it doesn't classify under SO:deletion because this class is defined as "the point at which one or more contiguous nucleotides were excised". A 'deletion' resulting from the loss of a complete chromosome, typically as the result of a meiotic non-disjunction event or unbalanced translocation. aneusomic chromosome exploratory term