The Calico Cat
Not only female!
- Calico is a tri-color pattern that can occur in nearly any domestic cat.
- Specifically domestic cats that show a range of colors.
- Not a breed!
- Due to color being related to the X chromosome, about 95% of Calico cats are female.
- No definitive historical background.
- However the calico pattern's existence has been traced to domestic cats along trade routes in Europe and Africa originating in Egypt.
Why typically in females?
- In female cats who have two X chromosomes, only one is usually used.
- The second one is shut down by X inactivation.
- The process called lyonization occurs, in which the shut down x chromosome super coils into a structure called a Barr body.
Lyonization leaves only one active X chromosome in each cell of the female embryo.
- When there are different alleles on each X (in this case orange, and black), the X that gets “turned off” is random in each individual cell leaving the other to be expressed.
- This is what causes the calico patterning.
Problem for males?
- The cause of male calicos (who are usually only XY) is the result of nondisjunction resulting in two different X chromosomes.
- The rare male Calico's are usually afflicted with Klinefelter's syndrome, which alters the chromosomes and usually results in infertility.
- Other effects of Klinefelter's syndrome are typical with lack of male hormone such as obesity.
- Due to the lack of hormone Male Calicos sometimes act feminine in behavior.
- Calico female cats have no ill health effects due to being Calico.
- The Calico pattern is caused by a sex linked co-dominant allele
- These are the possible Genotypes for the locus that determines coat color:
- Female cats can be orange XBXB, black XbXb, or calico XBXb
- Male cats can usually can only be black XBY or orange XbY.
- However in the case of a calico male, he inherited two X chromosomes in addition to his Y chromosome resulting in Klinefelter Syndrome.
Each cell in the male embryo undergoes Lyonization, just like the females cells.
- If the two X chromosomes do not have the the same allele the cat will be a calico.
- The Males genotype would then be XBXbY.
2. Malouf, N., Benirschke, K., & Hoefnagel, D. (1967). XX/XY chimerism in a tricolored male cat. Cytogenetic and Genome Research, 6(3-4), 228-241.
3. CENTERWALL, W. R., & Benirschke, K. (1973). Male Tortoiseshell and Calico (TC) Cats Animal models of sex chromosome mosaics, aneuploids, polyploids, and chimerics. Journal of Heredity, 64(5), 272-278.
4.The Genetics of Calico Cats. (n.d.). Retrieved April 29, 2016, from http://www.bio.miami.edu/dana/dox/calico.html