agr_zyg allelic state organellar plasmy Cells with a population of organelles from a single origin that all share the same organellar genome will contain only one allele of each organellar gene, while cells with populations of organelles of different origins may contain more than one allele of a given organellar gene. An allelic state that describes the number of different alleles of a gene from an organellar genome (i.e. mitochondrial, plastid) that may exist in a cell.