Question

The use of nucleotide sequence data to measure genetic variability is complicated by the fact that the genes of higher eukaryotes are complex in organization and contain \(5^{\prime}\) and \(3^{\prime}\) flanking regions as well as introns. Researchers have compared the nucleotide sequence of two cloned alleles of the \(\gamma\) -globin gene from a single individual and found a variation of 1 percent. Those differences include 13 substitutions of one nucleotide for another and 3 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?

Short answer

Answer: The observed changes in the cloned alleles of the gamma-globin gene do not occur in the gene's exons because of negative selection, which acts against harmful genetic changes in the coding regions. This prevents the spread of alleles that significantly impact protein structure or function. This observation does not necessarily change our concept of genetic variation, but it highlights the importance of considering the impact of changes in both coding and non-coding regions when studying genetic variation.

Step-by-step solution

To answer this question, we should first understand how genes are structured and what is meant by genetic variation. Genes are made up of coding regions (exons) and non-coding regions (introns), as well as flanking regions (\(5^{\prime}\) and \(3^{\prime}\)). The coding regions are translated into proteins, whereas the non-coding regions play various roles in regulating gene expression. Genetic variation refers to the differences in genes between individuals or populations, and it is often discussed in terms of nucleotide sequence differences. #Step 2: Consider the implications of changes in exons versus non-coding regions#

Since exons are the coding regions of a gene, any changes in the nucleotide sequence within these regions can potentially have a significant impact on the protein structure and function. This is because changes in the nucleotide sequence can lead to changes in the amino acid sequence of the protein, which can affect its folding, stability, and enzymatic activity. On the other hand, changes in the non-coding regions (introns and flanking regions) are less likely to have such a direct impact on the protein. These regions may still play roles in gene regulation, but alterations in these areas are usually less harmful to the organism. #Step 3: Explain why changes are not taking place in the exons#

Given this context, we can deduce that the reason why the observed changes do not take place in the exons is likely due to negative selection acting against such changes. Negative selection is a type of natural selection that removes deleterious alleles from a population; in this case, it prevents the spread of alleles with harmful changes in the coding regions. This means that genetic variants that cause significant changes in the protein structure or function are less likely to persist in the population. This is because individuals carrying such variants may have reduced fitness or may even die before they can reproduce and pass on these harmful variants. #Step 4: Discuss if this should change our concept of genetic variation#

While it is true that changes in the non-coding regions contribute to genetic variation, it does not necessarily mean that our overall concept of genetic variation should change. Genetic variation still encompasses differences in both coding and non-coding regions, with each type of variation having different implications for the organism. It is important to recognize that genetic variation can occur in both coding and non-coding regions and that each type of variation can have different effects on gene regulation, protein function, and overall organismal fitness. In this particular case, the observation underlines the importance of considering the impact of changes in both coding and non-coding regions when studying genetic variation.