Gene behind orange fur in cats

Original Article ↗ Hacker News Discussion ↗

Orange Cats and Behavior Stereotypes

  • Multiple anecdotes about orange cats being “silly,” “dog-like,” feistier, or “dumb,” but also stories of very smart orange cats.
  • Several commenters label the “one orange braincell” trope as internet folklore or confirmation bias.
  • One explanation offered: ~70% of orange cats are male, and male cats are described as more impulsive; correlation, not causation.
  • Others note that all coat colors show wide individual variation, with strong personalities reported for black, tortoiseshell, and Siamese cats as well.

Coat Color, Sex, and X‑Linked Genetics

  • Detailed explanation that orange/black coat color is X‑linked:
    • Female genotypes: XoXo (orange), XbXb (black), XoXb (tortoiseshell/calico).
    • Male genotypes: XoY (orange), XbY (black).
  • This yields roughly two-thirds of both orange and black cats being male in simple models, with real-world variation by colony.
  • Rare male tortoiseshells can arise via Klinefelter’s (XXY) or chimerism; linked resources on mosaicism and cat coat genetics.

“Gene for a Trait” Debate

  • Strong pushback on the phrase “gene for X” or “the gene behind X.”
  • Emphasis that genes are pleiotropic: they produce proteins that interact in many pathways, so a variant affecting fur color almost certainly has other roles.
  • Others argue this is partly semantic: saying a gene is “behind” a trait is acceptable shorthand when there’s strong causation or a clear mechanism.
  • Discussion likens genetic mutations to flipping bits in an executable: you see one clear effect but may have changed many behaviors.

Mechanism: ARHGAP36, MC1R, and GTP

  • MC1R is a GPCR controlling pigment production; ARHGAP36 is described as a GTPase activator that alters GTP levels.
  • More ARHGAP36 → lower GTP in melanocytes → reduced MC1R activity → shift toward lighter (orange/yellow) pigment instead of dark.
  • One commenter connects similar GPCR/GTP mechanisms to human mood disorders, long COVID/ME/CFS, and notes humans share these genes.

Cat Genetics Testing and Applications

  • UC Davis cat genetics lab is cited; some question the value of paying to genotype coat patterns when they are visible.
  • Others respond that visible traits are ideal for learning gene–trait relationships and for breeders, since similar colors can arise from different pathways.

Selection and Popularity of Coat Colors

  • Commenters note that humans shape cat evolution via preferences: adoption, sterilization, and (for some colors like black) higher euthanasia rates.
  • Orange cats may have spread because people find them “cute,” fitting a broader pattern of artificial selection on appearance.