The Calico Cat

Not only female!

History

  • 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.
Could calico cats be male?

Genetic transmission

  • 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.

Phenotype

Three distinct colors must be present for a cat to be considered a calico.


  • A Calico cat has tri color pattern of white with orange(or red or reddish-brown), and black (or grey or blue) patches on the coat.

Eradication

Because of this genetic anomaly not causing ill effects on females and is so rare in males there is no need for eradication methods. The problems posed in the rare Male calicos pose no threat and they typically live normal lives. Since responsible pet owners usually neuter/spay their animals the infertile nature of Calico males is actually a benefit.

Discussion point

Last week we discussed the ethics of genetic engineering, with Calico males being sterile it brings up the possibilities of genetically altering pets to be sterile. Though human genetic engineering is not ethically feasible in the near future, certainly there will be more experiments performed on animals. Do you think its the responsibility of scientists to genetically neuter their experimental animals? Perhaps inducing Kleinfelter's into the subject could act as an insurance that any other altered genes would not be propagated by accident.

References

1. Gould, L. (2008). Cats are Not Peas: A Calico History of Genetics. CRC Press.

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

5. http://www.cat-breeds-encyclopedia.com/Calico-cat.html

6. https://www.biologycorner.com/worksheets/genetics_calico_key.html