Final answer:
When crossing brown rabbits with very long legs (heterozygous for both traits) with white rabbits with very long legs (homozygous recessive for fur color and heterozygous for leg length), 50% of the offspring will have the desired phenotype of very long legs and white fur.
Step-by-step explanation:
To determine the percentage of offspring with very long legs and white fur from a cross between brown rabbits with very long legs and white rabbits with very long legs, you must consider the genotypes involved. Assuming that the leg gene and fur color gene are on different chromosomes, we know that the fur color gene has multiple alleles with the following dominance hierarchy: wild-type (brown fur) > chinchilla > Himalayan > albino (white fur). Since the question states that the rabbits have very long legs, they must be heterozygous for the leg gene as homozygosity would result in normal or very short legs.
For the fur color gene, a brown rabbit can only have the genotype bB (since the pure brown color is not mentioned as an option), and a white rabbit must be bb (albino). When crossing bB (brown fur) with bb (white fur) rabbits, you will get the following genotype ratios for fur color: 50% Bb (brown) and 50% bb (white). Since all rabbits have very long legs and are therefore heterozygous for that trait, all offspring will also have very long legs.
Combining these probabilities, 100% of the offspring will have very long legs, but only 50% will have white fur. Therefore, 50% of the offspring would be expected to have very long legs and white fur.