Understanding Crested Gecko Patterns and their interactions enables breeders to create pairings with intention. While the inheritability of each particular gene discussed below behaves in a predictable Mendelian fashion, these genes also come together to influence Pattern in a Polygenic manner. More simply put, all pattern genes interact with one another to influence the end result.
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Tiger
Vertical Pattern Influence
Aptly named, Tiger is renowned for its striking vertical bands of contrasting color. Initially recognized as a pattern in the mid-1990s, the term “Tiger” has undergone a semantic shift, now encompassing both the Tiger morph and the underlying Tiger force. This 'Tiger force' primarily drives the formation of contrasting vertical bands that separate different Base Colors, making Tiger expression highly dependent on the specific combination of Base Colors present. While the Yellow Base Color is most visibly impacted by the Tiger Pattern, its influence can be observed in the absence of Yellow (which will be discussed shortly). Tiger exhibits Incomplete Dominance in its inheritance and demonstrates a polygenic relationship with the Pinstripe pattern, highlighting a significant interaction between these two genetic factors.
The absence of the Tiger gene in geckos leads to a more consistent and uniform color. When breeding a 'Non-Tigered' gecko with a 'Tigered' one, the outcome is influenced by the number of Tiger genes present in the Tigered parent. A Tigered gecko with two copies of the gene (homozygous) will consistently produce offspring exhibiting some degree of Tiger patterning. In contrast, a Tigered gecko with only one copy of the gene (heterozygous) has a 50% chance of producing offspring that inherit the Tiger gene and display the pattern, while the other 50% will lack the gene and exhibit a more uniform coloration. This demonstrates the principles of Mendelian genetics, where the inheritance of traits is determined by the specific combination of genes inherited from both parents.
Horizontal Pattern Influence
Pinstripe
Similar to Tiger, the term 'Pinstripe' has evolved to encompass both a specific phenotype and a broader influence on color and/or pattern expression. The primary characteristic associated with Pinstripe is the presence of parallel rows of enlarged scales along the dorsal region (gecko's back). Contemporary homozygous Pinstripe individuals (two copies of the gene) often exhibit an additional row of enlarged scales along the mid-lateral area, collectively referred to as 'Quad Stripe'. The 'Pinstripe force' exerts a predominantly horizontal influence (snout to tail) on Base Color and other pattern expressions, with this influence largely confined to the Dorsal region. .
Tiger Vs. Pinstripe
Pattern's Polygenic Interaction
Tiger and Pinstripe patterns in crested geckos exhibit an antagonistic interaction. Tiger exerts a vertical influence, while Pinstripe counteracts this verticality. The full expression of either trait is most pronounced when the opposing influence is absent. This dynamic interplay exemplifies a polygenic trait, where the overall pattern is influenced by the combined effects of the multiple genes involved.
The results of this interaction can be partially visualized using a two-gene interaction model (see example). The Punnett Square depicts all possible combinations of alleles (different forms of a gene) inherited from the parents. The square demonstrates that multiple genetic pathways can lead to the same visual outcome, highlighted in gray are the genetic contributions an individual is capable of passing down to their offspring.
If both the Tiger and Pinstripe genes are present in an individual gecko, the interaction between them can often results in 'breaks', or gaps in the rows of enlarged scales. These do not indicate a less desirable version of the Pinstripe gene, but simply show us the Polygenic relationship between Tiger and Pinstripe in action.
The gecko pictured below highlights both the horizontal influence of Pinstripe (within the Dorsal region), and the vertical influence of Tiger (dark bands of underlying Base Color). Collectively, these patterns can often provide us insight into what Base Colors a particular gecko carries within its genotype. More on Base Color can be found here. (coming soon)
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Harlequin
Color and Pattern Modifier
The Harlequin gene significantly influences pattern and pigment expression. It behaves as a modifier gene by spatially separating the yellow base color into distinct dorsal and lateral regions, termed "Harlequin regions." The template for these regions is primarily shaped by the Pinstripe and Tiger interaction discussed above, which dictate Harlequin's spatial arrangement and resulting morphology.
Harlequin inheritance is dependent on the presence of a Yellow base color allele. This consistent association enables tracking of the trait and thus proof of this relationship. Individuals lacking the Harlequin gene exhibit a distinct phenotype termed "Phantom." For a deeper dive into the research and discovery of this relationship the entire research article can be found here. (01/2025)
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Because of the drastic impact Harlequin creates upon the phenotype, this gene has been selected for throughout the history of the hobby to encompass several forms that highlight certain characteristics. Some Harlequin versions are accompanied by various shades of White Pattern that have been steadily selected for both their brilliance and high amounts of coverage from the very early days of the hobby until now. Other, perhaps rarer forms remain a more accurate representation of the Yellow Base Color the gene impacts.
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