Mapping of quantitative trait loci for seminal vesicle mass and litter size to rat chromosome 8

The spontaneously hypertensive rat (SHR) and the Brown Norway (BN) rat diff er significantly in litter size (7.6 versus 4.5 pups). Ln the HXB and BXH s ets of recombinant inbred (RI) strains derived from SHR and BN rats, herita bility of litter size and of selected male reproductive parameters such as sperm production, sperm count, sperm morphology and motility, and the mass of the testis, epididymides, and seminal vesicles were estimated and a sear ch was undertaken for quantitative trait loci (QTL) associated with these p henotypes. The mass of seminal vesicles was significantly associated with a QTL near the D8Cebr204S21 marker on chromosome 8 (LOD score = 4.1, P = 0.0 0001); this QTL was responsible for 46% of the genetic variability of the t rait. The same gene marker on chromosome 8 also showed a suggestive associa tion with the litter size. Litter size was significantly correlated with th e mass of seminal vesicles (r = 0.58, P = 0.003). These findings indicate t hat the variability in litter size among RI strains may be due in part to d ifferences in the mass of seminal vesicles and it is possible that both mas s of seminal vesicles and litter size are determined by a pleiotropic effec t of the same QTL on rat chromosome 8.