Orange cats tend to be male, more often than not. This is because black fur and orange fur are both X-linked. So a male that gets one orange-X is gonna be orange, but a female that gets an orange-X might be orange or might be calico, depending on whether her other X is orange or black. So sayeth the books and websites, and mostly that makes sense. But…
What about black cats? Black females also need to be homozygous. Shouldn’t the same mechanism also give black cats the same lopsided sex ratio? No one ever says, “That cat is black, he’s probably a tom”, at least not that I’ve ever seen.
I’ve had two orange cats, both male, one calico and one tortie, both female, and two black, both female.
I think I remember reading somewhere that black and white cats, with equal parts of black and white, tend to be male. We had one when I was a kid who was male.
The gene responsible for giving orange fur O is sex-linked, found on the X chromosome. Males have only one X chromosome and thus have only one allele of the gene; hence O will give orange fur and o will give non-orange fur. Females have two X chromosomes and thus have two alleles; OO gives orange fur, oo give non-orange, while Oo results in a tortoiseshell pattern where some parts are orange and other parts are non-orange.
The black gene B is not sex-linked. Its recessive allele b causes brown. There’s a variant b[sup]l[/sup] for light brown. The orange color, if present, completely replaces black. Hence a male cat BB which would otherwise be black would show orange if it has the O allele.
Tables 4 and 8 in Robinson appear to bear out your assertion that no possible pairing can produce more black females than males, and therefore among the black variants more individuals must be male, but I feel like we are missing crucial information about the actual prevalence of the different alleles in the population in question before we can say how many more.
As noted the black gene isn’t sex-linked, so their shouldn’t be any confusion on that front.
The proportion of orange cats skews male due to it being sex-linked, but it skews more heavily male than it should and that is down to the position of the relevant gene on the X chromosome. Basically if the orange gene is in play a male should have a 1 in 2 chance of being orange - either it has the dominant orange gene on the X chromosome or it doesn’t ( either O=orange or o=not orange ). A female though should have a 1 in 4 chance of being orange - ( OO=orange, Oo=calico, oO=calico or oo=not orange ). With those odds you should get roughly 2 male orange cats for every female.
But it doesn’t actually work like that, because due to its odd position on the X chromosome as above, it is more than usually vulnerable to being damaged during meiosis which serves to winnow out the chance of getting an intact copy. So what actually happens given the presence of the orange gene in a parent is a 3 in 10 shot at an orange male and a 1 in 10 shot at an orange female. Leading to 3/4 of orange cats being toms.
Since it isn’t a sex-linked characteristic, it should be roughly 50/50 far as I know.
But I may not know very far :). Cat color genetics can get rather complex with various exceptions and overrides and as much as I’ve dug into the topic out of curiosity, I’m pretty sure I still don’t have it all down. Heck, I think there are three completely different ways of getting a seemingly pure white cat and the least likely of those ( albino ) comes with various sub-iterations ( i.e. incomplete blue-eyed vs. red-eyed ).
You mean not-orange, not-tortoiseshell. A very naive calculation would give 2/3 male, 1/3 female, but that is like counting spherical cows.
Just for instance, an Oo female might appear black because no orange patches happen to form. (And is it really so fair to say that all cats are either male or female without mentioning possibilities like XO, XXY, and mosaics?)
I’m having a hard time sussing out your reasoning here ( not a jab, I’m just easily confused ). To restate:
Orange cats - ~3/4 male as described above, due to linkage on the X chromosome.
Calico cats - almost 100% female for the same reason. You need to XX chromosomes to form a mosaic with orange, which only is possible with females and rare, usually sterile Klinefelter’s Syndrome males ( XXY ).
All other cat colors - no sex linkage to color. So since Fisher’s Principle describes the sex ratio in most mammals, presumably all other colors should be more or less randomly distributed at a roughly 1:1 distribution of males to females. Some colors might be more or less common, but they should be more or less common at an even sex ratio.
). To restate: