Many color varieties of the guppy, Poecilia reticulata, are commercially cultured in Singapore for the aquarium industry. In the group of guppy varieties called Snakeskin, males characteristically have snakeskin-like reticulations on the body and caudal fin. The snakeskin pattern on the body of male Snake-skin guppies is due to a Y-linked gene (Ssb). Female guppies, being homogametic (XX), do not carry the Ssb gene. About 90% of Yellow Snakeskin males have the typical snakeskin pattern on their bodies and tails. The remaining males are different in that the snakeskin body pattern has been modified into four or five vertical bars on the caudal-peduncle region. F₁ and F₂ results of single-pair reciprocal matings of the Yellow Snakeskin variety show that a single gene is responsible for the vertical bar pattern. This gene, bar, is autosomal recessive. In the homozygous condition (barbar), it interacts with the Y-linked Ssb gene to give vertical barring patterns on the caudal-peduncle of Yellow Snakeskin males. This pattern is not expressed when the dominant allele, bar , is present.