Rabbits of same species may have different genotypes and phenotypes which can be evident with the traits that is present. First, check if that particular species only has two fur colors. If so, we can say that one of the two fur colors may be the dominant trait and the other one may be the recessive. But one thing for sure is that the genetic code/s that affects the colors of the fur of the rabbits is different. Having a different genetic code means that there are different DNA sequences for the particular trait.
If the rabbits are from the same parents, you can conclude that the mother and father both carried at least one recessive gene.
For example, if black was the dominant gene, the genotypes for the black rabbit can be Aa or AA. Likewise, if brown was the recessive gene, the genotype for the brown rabbit must be aa.
For the parents to produce both brown and black rabbits, they must have one of the following combinations:
`"Aa" xx "Aa"`
`"Aa" xx "aa"`
AA x AA or AA x aa is not a possibility because it eliminates a chance for a brown rabbit. Likewise, aa x aa is not a possibility because it eliminates a chance for a black rabbit.