Chromosome variants in H. irritans. Mitotic plates from larval brain cells. a Two C-banded metaphases with karyotype XVIII, one with 2n=11 (2n=10+B) and the other with 2n=10 with free and attached B-chromosomes (white and black arrows respectively) b1 and b2 Hoechst 33258 stained metaphase and prometaphase of the same specimen with karyotype IV; arrows indicate rearranged pairs 1 and 2 c Hoechst 33258 stained metaphase and prometaphase c1 heteromorphisms of pairs 1 (dashed yellow arrow), 4 and 5 (dotted arrows) and the nucleolus close to chromosome 2 (dashed white arrow), expression of ribosomal DNA located on secondary constriction on chromosome 2 (white arrow) c2 H-banded karyotype with heteromorphisms; arrows indicate rearrangements on prometaphase chromosomes d C-banded incomplete metaphase with chromosomal pairs 1 and 3 (dotted arrow); white arrow indicates pair 1 carrying heterozygous inversion.