Home » Pet Health » Genes and Cancer » Genomes, Genotypes and Phenotypes


The genome describes an organism’s complete DNA within a cell, including all the genes in chromosomes that parents transmit to their offspring. The genome includes the hereditary instructions required for creating and maintaining life and differs for different species. Most of the genome sits in chromosomes in the nucleus (nuclear genome). However, a small amount of the genome lies outside the nucleus in the energy-producing structure called the mitochondrion (mitochondrial genome). Nitrogen-containing bases create pairs that form the DNA structure. The human genome contains approximately 3 billion base pairs, while dogs have about 2.5 billion and cats have 2.7 billion.

When comparing genotype and phenotype, simply put, a phenotype is the observable physical appearance, while a genotype is the unobservable genes that are responsible for such characteristics. Specifically, genotype refers to the two alleles (different versions of a gene) an organism has inherited for a particular gene of a trait. Therefore, there can be a separate genotype for traits like hair color, disease state, eye color, etc. The genotype is unique to every human and animal (except for most identical twins), and the genotypes of parents influence the genotypes of their offspring. As a result, scientists use genotyping to learn more about the origin of certain traits. For example, one study reports that genotyping reveals that bone size and body weight of large dogs are linked to 3 genes on the X-chromosome. Additionally, researchers have reviewed several studies demonstrating the genetic origin of common and rare cancer types of domestic cats.

The phenotype is the outcome of the expression of the genes and depends on genotype and environmental factors. For example, we can observe a dog’s coat color, tail length, eye color, and body size but not the underlying genes or proteins that contribute to these observable characteristics. Diseases also have their phenotypes. In cancer, the disease phenotype may include the observable attributes of tumor size and density. Some studies suggest that cancer prognosis in your pet can be determined by the observable features rather than genetics alone.

Learning the genetics of cancer and the influence of genotype and phenotype helps you to understand more about your pet’s cancer. You can speak confidently with your vet about the genetic basis of your pet’s cancer and appreciate what treatments work best for your furry friend, giving you many happy tomorrows together.

The Pet Cancer Foundation’s Website Editorial team is comprised of veterinarians, veterinary oncologists, and veterinary technicians, as well as scientific writers and editors who have attained their PhD’s in the life sciences, along with general editors and research assistants. All content found in this section goes through an extensive process with multiple review stages, to ensure this extended resource provides pet families with the most up-to-date information publicly available.

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Last Updated: November 10, 2022

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The following sources were referenced to write the content on this page: 

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Ludwig, L, Dobromylskyj, M, Wood, GA & van der Weyden, L 2022, ‘Feline oncogenomics: what do we know about the genetics of cancer in domestic cats?’, Vet Sci, vol. 9, no. 10, pp. 547-565

National Research Council, 2000, Scientific Frontiers in Developmental Toxicology and Risk Assessment. Washington, DC: The National Academies Press, viewed May 20, 2022, https://doi.org/10.17226/9871.

Plassais, J, Rimbault, M, Williams, FJ, Davis, BW, Schoenebeck, JJ & Ostrander EA 2017, ‘Analysis of large versus small dogs reveals three genes on the canine X chromosome associated with body weight, muscling and back fat thickness’, PLoS Genet vol. 13, no. 3, p. e1006661.

Roccabianca, P, Avallone, G, Rodriguez, A, Crippa, L, Lepri, E, Giudice, C, Caniatti, M, Moore, PF & Affolter, VK 2016, ‘Cutaneous Lymphoma at Injection Sites: Pathological, Immunophenotypical, and Molecular Characterization in 17 Cats’, Vet Pathol, vol. 53, no. 4, pp. 823-32.

Varallo, GR, Gelaleti, GB, Maschio-Signorini, LB, Moschetta, MG, Lopes, JR, De Nardi, AB, Tinucci-Costa, M, Rocha, RM, & De Campos Zuccari, DAP 2019, ‘Prognostic phenotypic classification for canine mammary tumors’, Oncol Lett, vol. 18, no. 16, pp. 6545-6553.

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