Genotype: Your dog’s genotype is her genetic makeup, or the complete collection of genes that she has in her DNA. Some parts of the genotype are responsible for how she looks, such as her size and hair color. Other parts are responsible for her behavioral traits and her health. The genotype also includes genes that we may not be able to observe, such as recessive traits that are overpowered by a more dominant trait (this is why two people with brown eyes can have a child with blue eyes – if both parents carry the alleles for both blue and brown eyes, they will have brown eyes but could pass on the gene for blue eyes to their child). Genotype can be important for dogs with cancer, because we can sometimes test for particular genetic mutations that make the cancer more responsive to specific treatments.