The use of nucleotide sequence data to measure genetic variability is complicated by the fact that the genes of many eukaryotes are complex in organization and contain 5' and 3' flanking regions as well as introns. Researchers have compared the nucleotide sequence of two cloned alleles of the γ-globin gene from a single individual and found a variation of 1 percent. Those differences include 13 substitutions of one nucleotide for another and three short DNA segments that have been inserted in one allele or deleted in the other. None of the changes takes place in the gene's exons (coding regions). Why do you think this is so, and should it change our concept of genetic variation?

Key Concepts

Genetic Variation

Genetic variation refers to the differences in DNA sequences among individuals within a population. This variation can arise from mutations, gene flow, and sexual reproduction. Understanding genetic variation is crucial for studying evolution, population genetics, and the inheritance of traits, as it provides the raw material for natural selection and adaptation.

Introns and Exons

Introns are non-coding regions of a gene that are transcribed into RNA but are removed during RNA processing, while exons are the coding sequences that remain and are translated into proteins. The presence of introns can contribute to genetic variability without affecting the protein-coding sequence, as changes in introns may not alter the function of the resulting protein, which explains why variations may occur outside of exons.

Flanking Regions

Flanking regions are sequences of DNA located adjacent to a gene, including 5' and 3' untranslated regions (UTRs) that can influence gene expression and regulation. These regions can harbor regulatory elements that affect transcription and translation, and variations in these areas can lead to differences in gene expression without altering the protein's amino acid sequence, further complicating the assessment of genetic variability.