O locus / orange coat colour (ARHGAP36-related) - Cat

O locus / orange in cats

This DNA test assesses the X-linked deletion in ARHGAP36 that causes orange coat colour in cats. The trait is also known as O locus, orange, red, ginger, tortoiseshell, calico and patched coat. The variant suppresses black-brown pigmentation in favour of orange pigment, so male cats with the orange allele are usually orange or ginger, while female cats with one orange allele often show tortoiseshell, calico or patched patterns.

Because this trait is X-linked, the visible outcome depends strongly on recorded sex and X-inactivation. Other colour genes, white spotting and pattern loci can further modify the final coat pattern.

How to read the result

• No orange allele: the tested O-locus deletion is not detected.
• One orange allele: in a male cat this usually causes orange/ginger; in a female cat this often causes tortoiseshell, calico or patched colouring.
• Two orange alleles: in a female cat this usually causes a fully orange/ginger coat, depending on other colour and pattern loci.

Practical value of this test

• shows whether the X-linked orange allele is present;
• supports genetic interpretation of tortoiseshell, calico, patched and ginger patterns;
• makes breeding plans and colour expectations more concrete when sex and other colour genes are also known.