A cat exhibiting characteristics of both sexes is a result of rare biological phenomena known as Disorders of Sexual Development (DSDs). While most animals develop clearly defined sexual anatomy, genetic and developmental anomalies can occasionally result in a mixed presentation. These variations are complex conditions arising from errors in genetic programming or hormonal signaling during embryonic growth. Observation of unusual coat colors or ambiguous external features often prompts investigation into these unusual occurrences.
Standard Feline Sex Determination
Sexual identity in cats, as in most mammals, is established by sex chromosomes. A typical female cat possesses two X chromosomes (XX), while a male cat carries one X and one Y chromosome (XY). The presence of the Y chromosome is the determining factor, as it carries the SRY (Sex-determining Region Y) gene.
The SRY gene acts as the molecular switch for the developing embryo. If the gene is present and functional, the undifferentiated reproductive tissue develops into testes. In the absence of the Y chromosome and the SRY gene, development defaults to the female pathway, leading to the formation of ovaries.
Disorders of Sexual Development in Cats
When the chromosomal, gonadal, or anatomical sex does not align with the standard pattern, the condition is classified as a Disorder of Sexual Development (DSD). These congenital anomalies occur when the typical sequence of sexual differentiation is disrupted. DSDs are categorized based on the cat’s sex chromosomes, gonadal tissue type, and the appearance of the external and internal genitalia.
One specific type is true ovotesticular DSD, where the cat possesses both ovarian and testicular tissue. This tissue is often combined into a single organ called an ovotestis. These cats may have a mix of male and female internal reproductive tracts, sometimes identified during a spay or neuter procedure.
Another category is pseudohermaphroditism, where the gonads match the chromosomal sex, but the external genitalia resemble the opposite sex. For example, an XY cat with testes may develop external genitalia that appear feminine due to a lack of response to male hormones. Conversely, an XX cat with ovaries might develop masculine-appearing external features due to exposure to abnormal hormone levels during development.
The XXY Chromosomal Anomaly
The most commonly discussed example of a cat exhibiting mixed sexual characteristics is the male Calico or Tortoiseshell cat. This phenotype is almost always linked to a specific chromosomal anomaly where the cat possesses an extra X chromosome, resulting in an XXY genetic configuration instead of the typical XY. This condition is comparable to Klinefelter Syndrome in humans and is a form of sex chromosome DSD.
The extra X chromosome allows these rare males to display the tri-color (Calico) or mottled (Tortoiseshell) coat pattern, which is typically exclusive to females. The genes for black and orange coat colors are X-linked. Since males normally have only one X chromosome, they can only express one color, but the presence of two X chromosomes allows for the expression of both.
The XXY makeup disrupts normal reproductive development, causing the cat to be phenotypically male but sterile. The surplus chromosome prevents the proper formation and maturation of sperm. These cats may also exhibit subtle physical differences, such as underdeveloped testicles, and are often prone to other health concerns related to the chromosomal imbalance. Estimates suggest that only about one in every 3,000 Calico cats is male, underscoring the rarity of this genetic event.
How Intersex Conditions Are Diagnosed
Diagnosing a DSD typically begins with a thorough physical examination, especially if the cat presents with ambiguous external genitalia or an unusual coat color for a male. Undescended testicles, or cryptorchidism, are a common finding that prompts further investigation. Because many DSDs are not immediately obvious, they may only be discovered during a routine spay or neuter surgery or when a cat presents for infertility issues.
A definitive diagnosis requires advanced testing to determine the underlying biological sex. Hormone testing can measure levels of sex steroids to check for imbalances or lack of response, which can indicate certain DSD types. The most conclusive test is karyotyping, which involves analyzing the cat’s chromosomes to confirm the number and arrangement of the sex chromosomes (XX, XY, XXY, etc.). Management of cats with DSDs is highly individualized, but many are sterilized to prevent potential health complications, such as tumor development in abnormal gonadal tissue.