Same, but Different Looking at your own family, you likely see plenty of variation in physical appearance—even among parents and siblings. Dogs are no different! During egg and sperm cell production, chromosomes swap various pieces of DNA. This process (called genetic recombination) happens as genes pass from one generation to the next, determining which traits get inherited. Because of the random nature of gene inheritance, DNA test results for siblings may report a slightly different mix of breeds. The pups shown here are a great example, as they’re from the same mother.