When the black coloured guinea pig (BB) is crossed with white coloured guinea pig (bb):
Parents: BB x bb
Gametes: B, B x b, b
F1 generation: All Bb (black coloured guinea pig)
Selfing: Bb x Bb
Gametes: b, b x B, b
F2 generation: BB, Bb, Bb and bb
The offsprings produced in the F2 generation are:
BB- black coloured guinea pig
2 Bb- black coloured guinea pig
bb- white coloured guinea pig
The genotypic ratio is 1:2:1. (1 BB, 2Bb and 1 bb)
The phenotypic ratio is 3:1 (3 black and 1 white)