Latent lines

Where a dominant blue eye appears with no coded parent, who must have carried it unseen, and which cats a single test would settle

The material on this page is drawn from the Global Cat Health Survey 2026, which is where its sources and its declarations of interest are set out in full.

Latent lines

A dominant allele cannot skip a generation. Where a cat in this register shows a dominant blue or odd eye and neither recorded parent shows one, one of those two parents carried it unseen, and so did a run of cats above that parent as far back as the trait goes. Nothing on a pedigree marks any of them, because they are coded for coat alone.

None of this is typed into the register. It is derived from the recorded parentage every time this site is built, so it cannot go stale as records are added, and it is stated as a deduction from dominance rather than as a claim by any source. A new mutation arising in the blue-eyed cat itself would satisfy the pedigree with no carrier at all. That is rare and it is not excluded here.

Where the trait appears with no coded parent

53 cats in this register show a dominant blue or odd eye while both recorded parents show none. Each is a point at which the trait becomes visible again after travelling unseen.

Possible carriers by descent, and of what 363 cats

These cats show no blue or odd eye and descend from a cat that carries. A heterozygous parent passes the variant to about half its offspring, so descent puts an animal on the list worth testing and only a laboratory takes it off. The last column names the variant or the line each one could be carrying, because a warning that does not say what to test for cannot be acted on.

144 of the 363 have a variant or a line standing in their own recorded ancestry, found by walking the parent links upward from each cat. That column is what says which test to buy. Where it is empty the register holds nothing above the animal, which is a gap in the pedigrees supplied and not a finding about the cat.

Obligate carriers 3 cats

Each of these shows no blue or odd eye and has produced cats that do, by two or more mates that show none either. On the pedigree it is the only common factor, so it carries. A laboratory result would confirm it and nothing else will. The last column gives the offspring and the number of mates.

One of the 3 has a variant or a line standing in its own recorded ancestry, found by walking the parent links upward from each cat. That column is what says which test to buy. Where it is empty the register holds nothing above the animal, which is a gap in the pedigrees supplied and not a finding about the cat.

Obligate pairs 74 cats

A cat showing the trait has these two as its recorded parents and neither shows it, so one of the two carried it unseen. The register does not say which, and testing one settles both, which makes these the cheapest tests in the register. The last column gives the mate and the cat that shows.

15 of the 74 have a variant or a line standing in their own recorded ancestry, found by walking the parent links upward from each cat. That column is what says which test to buy. Where it is empty the register holds nothing above the animal, which is a gap in the pedigrees supplied and not a finding about the cat.

On the path above a pair 1006 cats

Each of these stands above a cat that shows the trait although neither of its recorded parents does. The variant came down one branch of that ancestry and the register cannot say which, so these are candidates and not carriers. They are listed because a line that is never looked at is a line that is never found.