Question

when the mating of black and white rat takes place< all the offsprings produce in the first generation are black. why there are no white rats?

Answer 1

Answer:

All the offsprings are black this concludes that in rast black colour of the body is a dominant trait and white colour is a recessive trait.

If you got the concept of dominant trait, so a second reason can be that both the rats have homologous pair of alleles (same alleles). eg: (b,b) (B,B)

Let 'B' (for black colour trait) & 'b' (for white colour trait):

                                 B  +   b

                                     ↓

                                  (B,b)

As we know that 'B' i.e. black is a dominant trait so offspring (B,b) will be black in colour.