Why are only female cats tricolor and not male cats? - briefly
The phenomenon of calico cats being predominantly female is due to the genetic makeup of coat color inheritance in felines. Since coat color is determined by X chromosomes and males have only one X chromosome, they cannot express three colors simultaneously as females can with their two X chromosomes.
Why are only female cats tricolor and not male cats? - in detail
The phenomenon of tricolored fur in felines is an intriguing aspect of genetics, specifically related to sex chromosomes. Cats possess two types of chromosomes that determine their sex: XX for females and XY for males. The gene responsible for coat color, known as the O (Orange) gene, is located on the X chromosome.
In female cats with XX chromosomes, each X chromosome can carry a different allele for the O gene. If one X chromosome carries the dominant orange allele (O) and the other carries the recessive non-orange allele (o), the cat will express both colors on her fur, resulting in a tricolored coat. This is because the expression of the X-linked genes can vary due to a process called X-inactivation, where one of the two X chromosomes in each cell is randomly silenced early in development. As a result, some cells will express the orange allele while others express the non-orange allele, leading to a mosaic pattern of colors.
Male cats, with their XY chromosome composition, have only one X chromosome. If this X chromosome carries the dominant orange allele (O), the cat will be orange. Conversely, if it carries the recessive non-orange allele (o), the cat will not exhibit orange fur. Since male cats lack a second X chromosome to carry a different allele, they cannot express tricolored coats.
Additionally, the presence of the gene for black fur, which is located on a separate autosomal chromosome and not linked to sex, contributes to the diversity of coat colors. When this gene is active alongside the X-linked orange allele in female cats, it can result in a tortoiseshell pattern (black and orange) or a calico pattern (black, orange, and white), both of which are forms of tricoloring.
In summary, the genetic makeup of female cats allows for the expression of multiple coat colors due to the presence of two X chromosomes, while male cats, with only one X chromosome, cannot exhibit this variation. This is why tricolored coats are predominantly observed in female cats.