Homologous chromosomes can be distinguished by restriction fragments if their
nucleotide sequences differ in the restriction sites.
On chromosome A, three cutting sites generate fragments of 7 kb and 3 kb.
On chromosome B, two cutting sites generate a single 10 kb fragment.
The possible genotypes, AA, AB, and BB, produce restriction fragment-length polymorphisms (RFLPs), which can be identified on a Southern blot.