WHAT ARE SEX-LINKED TRAITS?
There are two groups of chromosome pairs: non-sex chromosomes (called autosomal) and sex chromosomes. A sex chromosome is a type of chromosome that participates in sex determination, and all other chromosomes are autosomal. There is only one pair of sex chromosomes, the X and Y. Females have two X chromosomes, one inherited from each parent. Males have one X chromosome (inherited from the mother) and one Y chromosome (inherited from the father). Humans, dogs, and cats all have a single pair of sex chromosomes, but the number of autosomal chromosomes varies:
| Species | Pairs of Autosomal Chromosomes |
| Human | 22 |
| Dog | 38 |
| Cat | 18 |
Genes found on sex chromosomes are known as sex-linked traits because the effects of these genes depend on the sex of an individual.
Females are XX, so they have two copies of X-linked genes, and males are XY and thus have one copy of an X-linked gene. X-linked traits are present in both males and females (as they both carry X chromosomes), while only males show Y-linked traits (only passed from father to son).
Sex-linked diseases result from mutations in genes on the X or Y chromosome. Most X-linked diseases in humans and animals are more likely to affect males because a male has only one X chromosome. Females who inherit an X chromosome with a mutated gene also have an X chromosome from the other parent, giving them a chance to have one normal copy of the gene. For females to have the sex-linked disease, they must therefore inherit two defective copies of an X-linked gene mutation. Females with only one defective copy of an X-linked gene are carriers of X-linked diseases and do not express symptoms. As a result, we often do not know when we are carriers of a sex-linked disease.
An example of an X-linked disorder that occurs in humans and dogs is Hemophilia A. It is a bleeding disorder where blood doesn’t clot properly, which leads to excessive bleeding that can damage organs and tissues. Because it is X-linked, the disease is more prevalent in male animals than in females.
Learning about genetics and how chromosomes can impact disease likelihood helps you understand your pet’s risk. It also gives you the knowledge to discuss treatment options with your vet if your pet is diagnosed with a genetic disease like cancer.
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: October 30, 2022
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The following sources were referenced to write the content on this page:
Farwick, NM, Klopfleisch, R, Gruber, AD & Weiss AT 2017, ‘Microsatellites within the feline androgen receptor are suitable for X chromosome-linked clonality testing in archival material’, J Feline Med Surg, vol. 19, no. 4, pp. 454-460.
Lozier, JN & Nichols, TC 2013, ‘Animal models of hemophilia and related bleeding disorders’, Semin Hematol, vol. 50, no. 2, pp. 175-184.
Mochizuki, H, Goto-Koshino, Y, Takahashi, M, Fujino, Y, Ohno, K & Tsujimoto 2015, ‘Demonstration of the cell clonality in canine hematopoietic tumors by X-chromosome inactivation pattern analysis’, Vet Pathol, vol. 52, no. 1, pp. 61-69.
The Pet Cancer Foundation’s medical resource for pet owners is protected by copyright.
For reprint requests, please see our Content Usage Policy.