Then, during lyonization, if the X chromosome carrying a black fur allele is inactivated, the cell will produce orange fur. A cat must receive both of these alleles, one from each parent, in order to have fur with orange and black patches. One allele produces orange fur, and the other produces black fur. In cats, the X chromosome carries a gene that determines fur color, and there are two different versions (or alleles) of this gene in calico cats. Lyonization occurs during the embryonic development of every female mammal, including female cats, and it’s impossible to predict which of the two X chromosomes will be inactivated. It ensures that only one active X chromosome exists in the cell of a female embryo.
This random and irreversible process is known as Lyonization. Only the genes on the uncoiled X chromosome are expressed, which means that all physical traits (such as fur color and eye color) are produced by the genetic information of the active X chromosomes. Because the chromosome is curled up, its genes cannot be expressed. During embryonic development, one of the X chromosomes in each cell becomes inactive by coiling up into a tight structure known as a Barr body. For female felines, the process works a little differently because cells cannot receive instructions from two different X chromosomes. Lyonization: The Inactivation of X ChromosomesĮach cell of a biological male cat receives instructions from two chromosomes, one X and one Y. In 2018, a rare male calico cat was barred from competing in cat shows.) Strange, right? Not if you know how those distinctive orange, black, and white splotches are produced. A typical male cat with one of each sex chromosome (XY) cannot have a calico fur pattern, which means that almost all calico cats are female. Cats receive an X chromosome from their mother and either an X or Y chromosome from their father. Sex chromosomes work the same way in cats. This is why all humans have an X chromosome, but only some have a Y chromosome. The Y chromosome, on the other hand, doesn’t carry many genes, and none of its genes are necessary for the cell to survive. The X chromosome is large and carries hundreds of genes, some of which are essential for survival.
Understanding the Genetics of Calico Cats A Brief Overview of Sex Chromosomes More specifically, you can learn about epigenetics, or the study of changes in organisms due to the modification of gene expression, not the alteration of DNA. Known for their distinctive patches of black, orange, and white fur, calico cats illustrate a genetic process known as “lyonization.” Whether you adore cats or you’re allergic to them, you might be surprised to learn that you can better understand genetics by studying calico cats.
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