The genetics of catnip susceptibility

Question

In doing a little looking around, I found three different answers to the question: What percent of cats are susceptible to catnip?

• The Humane Society says "an estimated 50 percent"
• Scientific American says "about 70 to 80 percent"
• Cat World says "around 50–66%"

Each source carefully notes the figure as an estimate. None of them cite any sources or give any explanation beyond the figures coming from "experts." (You'd think someone would take a poll, but that's not my point)

I recall hearing many years ago that the gene for catnip sensitivity followed a simple dominant-recessive pattern. Similar to Mendel's peas, in a well-mixed population, you'll have the pairs RR, Rr, rR, and rr - only 25% (the rr group) will not express the trait, the other 75% will. That would lend support to Scientific American's numbers.

However, if the genes that cause catnip sensitivity exhibit some form of co-dominance, like human blood groups, then the percentages can skew.

So my question comes down to: What hard-science exists to explain the variation in sensitivity to catnip among cats? Have there been any long-term breeding experiments? Has that portion of the feline genome been explored at all?

Answer 1

You misunderstand how the percentages are applied in Mendellian genetics. Those expected percentages only work given known sets of genes in individuals. In real life, genes are often distributed very unevenly in a population, due to the pressures of natural selection, and the effect of isolation. An easily observable example is the gene for polydactylism (extra fingers) is dominant in humans. If the gene were evenly distributed in the human population, polydactyly would be common. Obviously this is not true, because the gene did not end up getting spread much beyond some isolated populations.

According to this document that is observing the results in breeding individual cats with known phenotypes, the catnip gene appears to be autosomally (not sex linked) dominant.