Answer:
B. Differences in the nucleotide sequences of genes are the genetic basis of coat-color variation in all cattle.
Step-by-step explanation:
The variation in coat color is determined by multiple genes, and the interaction between these genes determines the final color of the animal's coat. In cattle, the most important genes controlling coat color are the melanocortin 1 receptor (MC1R) and agouti signaling protein (ASIP). Different alleles (alternate forms of genes) of these genes can result in different coat colors and patterns. For example, the dominant allele of MC1R is responsible for black coat color, while the recessive allele is responsible for red or yellow coat color.