Describe a gene mutation as a random change in the base sequence of DNA, using sickle cell anaemia as an example

Sourav PanNovember 4, 2024

Answered

A gene mutation is defined as a random change in the base sequence of DNA, which can lead to alterations in the structure and function of proteins produced by that gene. One well-known example of a gene mutation is sickle cell anemia, which is caused by a specific mutation in the hemoglobin gene.

Understanding Gene Mutations

1. Nature of Gene Mutations:
   • Gene mutations can occur spontaneously during DNA replication or as a result of environmental factors such as radiation or chemical exposure. These mutations can involve various changes, including substitutions, insertions, or deletions of nucleotide bases.
2. Point Mutation:
   • The mutation responsible for sickle cell anemia is a type of point mutation known as a substitution. In this case, a single nucleotide in the DNA sequence is altered. Specifically, the mutation involves the replacement of adenine (A) with thymine (T) in the gene coding for the beta-globin subunit of hemoglobin.

Sickle Cell Anemia Example

1. Mutation Details:
   • The normal sequence of the hemoglobin gene includes the codon GAG, which codes for the amino acid glutamic acid. However, due to the mutation, this codon is changed to GTG, which codes for valine instead. This single amino acid substitution (glutamic acid to valine) occurs at position 6 of the beta-globin chain.
2. Effects on Hemoglobin:
   • The resulting variant of hemoglobin is known as hemoglobin S (HbS). Under low oxygen conditions, HbS molecules tend to aggregate and form rigid structures, causing red blood cells to adopt a characteristic sickle shape instead of their normal round shape. This altered shape can lead to blockages in blood vessels and reduced oxygen delivery to tissues.
3. Phenotypic Consequences:
   • Individuals with two copies of the sickle cell allele (homozygous for HbS) experience sickle cell anemia, which is characterized by severe symptoms such as pain crises, anemia, and increased risk of infections. However, individuals with one copy of the sickle cell allele (heterozygous) typically do not exhibit symptoms of the disease but are carriers and may have some resistance to malaria.