Porcupine (symbol p) is a recessive morphological mutation located at the p locus.
Homozygous porcupine (p//p) pigeons produce feathers that fail to open, remaining permanently in their sheaths. The enclosed feathers appear similar to the quills of a porcupine.
Porcupine is an autosomal recessive mutation. This means that both parents need to carry the mutant gene for it to express in the next generation. As a recessive mutation, it is possible for this trait to be carried by a bird who does not visually express it.