Genetics of the Spotted (Sp) allele

[Mathias Gabel]

Hi!   Some time ago, a reader of this mailinglist, reported that the entire offspring of a spotted pair were also spotted, although one third of the pubs would expected to be non-spotted:   Parents: Sp sp(+) x Sp sp(+)   Expected offspring: 1/4 Sp Sp (lethal before or shortly after birth) 2/4 Sp sp(+) (Spotted) 1/4 sp(+) sp(+) (Non-spotted)   So, littersize would be reduced and the survivors would be 2/3 spotted and 1/3 non-spotted.   I've recently paired a black spotted with a black non-spotted. They had 13 pups in three litters. The dominant character of Spotted would suggest, that half of them were spotted:   Parents: Sp sp(+) x sp(+) sp(+)   Expected offspring:   1/2 Sp sp(+) (Spotted) 1/2 sp(+) sp(+) (Non-spotted)   But that was not the case. Only three of them were spotted, the rest were solid black.   Has anyone in this group experienced a similar difference in the inheritance of the Spotted allele?