Question

In a recent study of cichlid fish inhabiting Lake Victoria in Africa, Nagl et al. (1998. Proc. Natl. Acad. Sci. IUSA/ 95: \(14,238-14,243\) ) examined suspected neutral sequence polymorphisms in noncoding genomic loci in 12 species and their putative river-living ancestors. At all loci, the same polymorphism was found in nearly all of the tested species from Lake Victoria, both lacustrine and riverine. Different polymorphisms at these loci were found in cichlids at other African lakes. (a) Why would you suspect neutral sequences to be located in noncoding genomic regions? (b) What conclusions can be drawn from these polymorphism data in terms of cichlid ancestry in these lakes?

Short answer

Answer: Neutral sequences are suspected to be located in noncoding genomic regions because they do not affect an organism's phenotype or fitness, and mutations in these regions do not result in significant alterations to the organism's functional proteins. Polymorphism data suggests that cichlid populations in Lake Victoria share a common ancestry and genetically diverged from cichlid populations in other African lakes. The presence of similar polymorphisms in both lacustrine and riverine cichlid species from Lake Victoria indicates they likely descended from a single ancestral population, while different polymorphisms in cichlids from other African lakes indicate distinct ancestral lineages that evolved separately.

Step-by-step solution

Part (a): Understanding Neutral Sequences and Noncoding Genomic Regions

Neutral sequences refer to DNA sequences that do not have any effect on an organism's phenotype or fitness. They may undergo mutations or change over time without affecting the organism's survival or ability to reproduce due to their lack of functional importance. Noncoding genomic regions are sections of DNA that do not produce proteins, meaning they are not translated into functional products like enzymes or structural proteins. Since neutral sequences do not affect an organism's phenotype or fitness, it would be reasonable to suspect that they are located within noncoding genomic regions, as any changes or mutations in these regions will not result in significant alterations to the organism's functional proteins or phenotype.

Part (b): Interpreting Polymorphism Data

The polymorphism data presented in the study reveals that the same polymorphism was found in nearly all tested species from Lake Victoria, both lacustrine (lake-dwelling) and riverine (river-dwelling), while different polymorphisms at these loci were found in cichlid species in other African lakes. This suggests that the cichlid populations in Lake Victoria share a common ancestry and genetically diverged from cichlid populations in other African lakes. Since both lacustrine and riverine cichlid species from Lake Victoria show the same polymorphisms, it implies that they likely descended from a single ancestral population that colonized the lake and then diverged into multiple species over time. The presence of different polymorphisms in cichlids from other African lakes indicates distinct ancestral lineages in those lakes, which evolved separately from the ancestral lineage in Lake Victoria.