Some stickleback fish develop protective spines, and other stickleback fish are spineless. Spine development is controlled by the expression of a gene known as Pitx1. The spineless phenotype is due to a mutation in Pitx1 that results in no expression of Pitx1 during development in regions where spines would otherwise form. When scientists compared the Pitx1 coding sequence in spined and spineless fish, they found this sequence was the same in both types of fish. Propose plausible hypotheses for the location of this mutation and for how it alters spine development.

Verified step by step guidance

1. Identify the role of Pitx1 gene: Understand that the Pitx1 gene is crucial for the development of spines in stickleback fish. It is responsible for the expression of certain proteins that lead to spine formation during the developmental stages of the fish.
2. Consider the genetic similarity: Since the coding sequence of the Pitx1 gene is the same in both spined and spineless fish, the mutation likely occurs in a non-coding region of the DNA. This could be in regulatory elements such as promoters or enhancers that control the expression of the Pitx1 gene.
3. Hypothesize the mutation's effect on gene expression: The mutation could be in a regulatory region that normally enhances or permits the expression of the Pitx1 gene in the regions where spines develop. In spineless fish, this mutation could inhibit or completely prevent the expression of Pitx1 in these regions, leading to the absence of spines.
4. Consider alternative splicing: Another hypothesis could be that the mutation affects the splicing of the Pitx1 mRNA, leading to an altered, non-functional protein that cannot induce spine development, even though the primary coding sequence is unchanged.
5. Propose experimental approaches: To test these hypotheses, scientists could perform genetic assays such as reporter gene assays to identify the activity of different regulatory regions, or RNA sequencing to detect any differences in the mRNA transcripts between spined and spineless fish.

Key Concepts

Gene Expression

Gene expression is the process by which information from a gene is used to synthesize functional gene products, typically proteins. In the case of the stickleback fish, the expression of the Pitx1 gene is crucial for spine development. If the gene is not expressed in certain regions during development, the corresponding structures, like spines, will not form, leading to the spineless phenotype.

Mutation

A mutation is a change in the DNA sequence that can affect gene function. In the context of the stickleback fish, a mutation in the Pitx1 gene leads to the absence of its expression in areas where spines would normally develop. Understanding the nature and location of this mutation is essential for explaining the phenotypic differences between spined and spineless fish.

Phenotypic Variation

Phenotypic variation refers to the observable differences in traits among individuals of a species, which can arise from genetic differences, environmental influences, or both. In stickleback fish, the presence or absence of spines represents a clear example of phenotypic variation, driven by the genetic regulation of the Pitx1 gene. Investigating how mutations affect this variation can provide insights into evolutionary adaptations.