Table 1. Reproductive efficiency of wild type and SP hyh mice.

Male	Female	Productive matingsa	Litter size	Number of litters	Relative fecundityb
wt	wt	90.9% (13/15)	7.5	5.1	34.76
het	het	89.7% (113/126)	7.3	5.4	35.35
hyh	het	0% 0/24	0.0	0.0	0.0
hyh	hyh	1.4% (2/148)c	5.5	4.5	0.33

wt: wild type (Napa^(+/+)); het: heterozygous (Napa^(hyh/+)); hyh: mutant homozygous (Napa^(hyh/hyh)) with the slow progressive phenotype.

^aMatings are considered “productive” if at least one offspring was born.

^b“Relative fecundity” is obtained as: (productive mating/100)×(litter size)×(number of litters); the value obtained is a measure of the overall fecundity according to the Handbook of Genetically Standardized JAX Mice [33].

^cThe same hyh male had two productive matings.