Why do tortoiseshell cats have mosaic fur patterns?
Context Tortoiseshell cats are known for their unique and striking fur patterns. This distinctive coloration is due to the fact that they possess a different melanin allele on each of their X chromosomes. One of these X chromosomes is inactivated through a process called Lyonization, resulting in a Barr Body. The other X chromosome remains active and expresses its corresponding melanin allele, determining the color of the fur produced by that specific cell. During cell division, daughter cells inherit the same activated X chromosome and suppress the same X chromosome in the Barr Body, leading to consistent fur color within a cell lineage. Consequently, we wouldn't expect to see a random distribution of fur colors across the cat's body. Instead, we observe contiguous areas of color, known as 'islands', where cells derived from the same progenitor cell share the same activated X chromosome. However, this raises a question: why do we also see what appear to be lines or pat...