20. Gene mutations. Mechanisms and mutagenic factors.
Covers what gene mutations are and how they are classified: by cell type, by effect on fitness, by structural change in DNA and by cause. It then explains the mechanisms behind substitutions, insertions and deletions, including slipped strand mispairing and intercalating agents, followed by external mutagenic factors. The note closes with how silent, missense, nonsense, frameshift, in-frame, splice-site and regulatory mutations affect protein structure and function. It includes mnemonics, a mutagen table, an effects summary table and examples such as sickle cell anaemia and progeria.
Topic 21 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 14 sections, about 1,129 words (9 min of reading), with 11 flashcards.
In this note
Gene Mutations. Mechanisms and mutagenic factors
What Are Gene Mutations?
Classification of Gene Mutations
Mechanisms of Gene Mutations
Mutagenic Factors (External Agents That Cause Mutations)
Effects of Gene Mutations on Protein Structure and Function
🔬 1. What Are Gene Mutations?
🧩 2. Classification of Gene Mutations
B. By Fitness Effect
C. By DNA Structural Change
D. By Cause
🔄 3. Mechanisms of Gene Mutations
☢ 4. Mutagenic Factors
🧬 5. Effects on Protein Structure/Function
What Are Gene Mutations?
Gene mutations are changes in the DNA sequence that occur without the cell's intentional control.
These changes typically involve small-scale alterations in one or a few nucleotides.
Mutations play a crucial role in evolution as they create new genetic variants, which natural selection can act upon.
Many mutations appear after the cell tries to repair chemical injuries to the DNA. While the DNA may survive the repair with a changed sequence, it cannot survive the initial damage itself.
Classification of Gene Mutations
A. Based on the Cell Type Affected and Inheritance
Somatic mutations occur in body cells and are not passed on to offspring unless reproduction is asexual.
Germ line mutations occur in reproductive cells and can be inherited by the next generation.
B. Based on Impact on an Organism’s Fitness
Harmful mutations reduce an organism’s chances of survival or reproduction.
Beneficial mutations improve fitness and offer a survival advantage.
Neutral mutations do not affect fitness but may still be passed on. They form the basis of the molecular clock due to their steady rate of occurrence.
Whether a mutation is helpful or harmful can depend on environmental conditions. The same mutation can be neutral in one setting and beneficial or harmful in another.
C. Based on the Structural Change in DNA
Substitution involves replacing one nucleotide with another.
Insertion adds an extra nucleotide to the sequence.
Deletion removes a nucleotide from the sequence.
D. Based on the Cause of Mutation
Spontaneous mutations occur naturally due to internal factors.
Induced mutations are caused by external agents called mutagens.
Continue reading free
The whole note, all 14 sections, is free with an AceMed account, with its 11 flashcards. Premium adds flashcard recall, highlights and Ask AI.
