Cats have 19 pairs of chromosomes. One member of each pair comes from mother and one from father. Along the chromosomes are genes. Genes provide the information necessary to produce a cat. All the genes in all the chromosomes comprise the genome, which is the complete cat blueprint. Each gene is also called a locus, indicating that it has a physical location on the chromosome. Thus, each cat has two alleles of each gene; one inherited from each parent. The genotype at a locus is a determined by the identities of those two alleles.
The sister cats will have genes that they have got from their mother and father which might have undergone crossing over and also epistasis. Thus, differentiating both the sisters.