We know that purebred means that the organism contains the same alleles for the trait and hybrid means that it contains two different alleles for the trait. Dominant means that it will be shown in a hybrid and a purebred, but recessive traits will only be shown in purebred recessive organisms.
a) The offspring of a purebred white (recessive) cow and a purebred brown (dominant) bull, would be all hybrid brown (dominant). This is because as I stated above, dominant traits are shown when the offspring has both dominant and recessive alleles for the same trait.
b) The offspring of a purebred brown (dominant) cow and a purebred brown (dominant) bull would all be purebred brown (dominant). This is because if both of the parents have only alleles that code for brown color, the only color that the offspring can be is brown.
c) The offspring of a purebred white (recessive) cow and a purebred white (recessive ) bull would all be purebred white (recessive), for the same reason stated above in part b), the only difference being that the alleles are recessive and code for white color instead of being dominant and coding for brown color.
d) The offspring of a hybrid brown (dominant) cow and a purebred white (recessive) bull would be half hybrid brown (dominant) and half purebred white (recessive). This can be seen best if you set up a Punnett Square, which is a diagram that shows allele frequencies in offspring. This shows you that the chance that the offspring get the dominant allele from the mother cow is 50%, thus 50% would be hybrid brown (dominant), as the father can contribute only a recessive white allele. The other 50% would be purebred white (recessive) because the mother cow would be contributing a white allele and so would the father.
