The present invention relates to a technology to provide segmental aneuploidy progeny strains of Trichoderma reesei. In particular, the present invention relates to a method to produce segmental aneuploidy progeny strains of Trichoderma reesei via sexual crossing of two parent haploid strains with chromosome heterozygosity (e.g. one having scaffold M and scaffold 33, the other having scaffold F and scaffold X), preferably at least one of which includes a non-homologous end joining (NHEJ) gene. The present invention also relates to stable, segmental aneuploidy progeny strains of richoderma reesei thus produced which particularly exhibit enhanced gene expression or activities of carbohydrate-active enzymes (CAZymes) and more particularly prevent returning to euploidy for an extended period of time.