Final answer:
Amelanistic corn snakes have a color variant due to a transposable element inserting into an intron of the OCA2 gene, disrupting normal gene function and leading to the absence of black and brown pigments, while red and yellow pigments remain unaffected.
Step-by-step explanation:
The question relates to an observed phenotype in corn snakes and the genetic cause behind it. Amelanistic corn snakes exhibit color variants due mainly to the absence of black and brown pigments, leaving only red and yellow pigments visible. The amelanism is caused by transposable elements interfering with gene function. When these elements insert themselves into an intron of a gene—in this case, the OCA2 gene, which is involved in the pigment production—the normal splicing process during mRNA maturation may be disrupted. Intron sequences are typically removed during mRNA splicing, but the presence of transposable elements can change how the intron is recognized. If the splicing machinery does not correctly remove the intron or if it incorrectly splices the mRNA, this can result in a nonfunctional protein or altered levels of the protein.
The OCA2 gene is critical for the synthesis of melanin, the pigment responsible for black and brown colors. If a transposable element disrupts the proper functioning of this gene, it can prevent the production of melanin, causing the amelanistic appearance in the affected snakes. The visible pattern of red and yellow pigments is because these are not affected by the mutation and can still be produced by the snake.