Mutations and Genetic Code

• Mutation is a sudden change in the DNA sequence.
• It causes a change in genotype, which may be expressed in phenotype.
• Mutation, along with recombination, produces variations and serves as raw material for evolution.

Types of Mutation:

• Loss of a DNA segment is called deletion.
• Gain of a DNA segment is called insertion or duplication.
• These changes may alter the chromosome.

Point Mutation:

• A change in a single base pair of DNA is called a point mutation.
• A well-known example is sickle cell anaemia.
• In this case, in the beta-globin gene, glutamate is replaced by valine.

Frameshift Mutation:

• Insertion or deletion of base pairs may cause frameshift mutations.
• If one or two bases are inserted or deleted, the reading frame changes from that point onward.
• These are called frameshift insertion or deletion mutations.

Insertion or Deletion of Three Bases:

• If three bases or multiples of three bases are inserted or deleted, one or more complete codons are added or removed.
• As a result, one or more amino acids are inserted or deleted.
• The reading frame remains unchanged.

Analogy:

• The triplet-word example is: RAM HAS RED CAP.
• Inserting one or two letters disturbs the grouping of three-letter words.
• Inserting three letters keeps the triplet pattern unchanged.

• A mutation is a sudden change in the DNA sequence that alters the genotype and provides raw material for evolution.
• It may involve deletion (loss) or insertion/duplication (gain) of a DNA segment.
• A point mutation changes a single base pair — e.g., in sickle cell anaemia, glutamate is replaced by valine in the beta-globin gene.
• A frameshift mutation (insertion/deletion of one or two bases) shifts the reading frame, while adding/removing three bases changes whole codons but keeps the frame intact.
• Analogy "RAM HAS RED CAP": one or two extra letters disturb the triplet grouping, but three extra letters keep it unchanged.