X-Chromosome Inactivation Explains Mosaic Patterns

Commenters point to it as the best short explanation of X inactivation and why calico cats and some human traits are mosaics.

Veritasium explains X-chromosome inactivation, where different cells in a woman's body switch off different X chromosomes, giving a mosaic pattern. It uses animation from the WEHI institute and connects to calico cat coloring.