I investigated the potential contribution of Y-linked genes by analyzing 16 Y-consomic strains that had been established on a DH-strain background. The results provided evidence that only the Y chromosome from the C3H/HeJ strain was different from most other inbred strains. The CBA strain has the lightest testis and the DDD strain has the heaviest testis among mouse strains; however, Y-consomic analysis revealed that there were no significant differences in testis weight among DH, DH-Chr Y^DDD, and DH-Chr Y^CBA strains, suggesting that Y^DDD and Y^CBA themselves do not influence testis weight. QTL analysis in DDD × DH F₂ mice identified significant testis weight QTLs on chromosomes 9, 14, and 17, and the DDD allele at all these loci was associated with an increase in testis weight. Contribution of Y chromosome itself to testis weight was thus rather modest, and therefore, major testis weight determinants are autosomal. However, it was uncertain whether there would be any effects by interactions between Y chromosomal and autosomal genes.

(Edited by Akira IRITANI, M.J.A.)