Dam blk Angus X Sire Red Gelbvieh = black heifer calf BB x bb = Heterozygous black heifer calf (Bb genotype)
Black calf now heifer X red Gelbvieh bull = tan(red) heifer calf Bb heifer x bb bull possible dilutor carrier = bb possible dilutor carrier homozygous red heifer
Blk calf (now cow) x (different) red Gelbvieh bull = light grey "silver" heifer calf.. Bb cow x bb bull = Bb homozygous heifer calf
Original blk Angus cow X 2nd red Gelbvieh bull = blk heifer calf BB cow x bb bull = Bb heifer heterozygous black
I hope this is clear enough, tried using the blue font color to highlight my text. In my opinion, the original red gelbvieh bull mated to the black angus cow is not a dilutor carrier. The red gelbvieh bull mated to the heterozygous black heifer is possibly a dilutor carrier. Where I am not certain is if the red gelbvieh bull mated to the heterozygous black cow (third mating) is the same bull mated to the original black angus cow (fourth mating). If it is the same bull, then I think the bull from the second mating is the only dilutor carrier. If third mating and fourth mating bull is a different bull, then the bull from the third mating is probably a dilutor carrier as well. Sound right? Whew!! Please feel free to correct me if I am wrong. Good exercise in genetics and heritability .