6.7 - Mutations

Mutations: Any change in a gene or chromosome. Mutations can result in changes in phenotype and can be positive, negative, or neutral, depending on the environmental context.

Inheritance of Mutations

• Germline Mutations: Must occur in sex cells (sperm or egg) to be inherited by offspring.

• Somatic Mutations: Occur in body cells and are not passed down to offspring.

Causes of Mutations

1. Random Events: Most mutations occur randomly during cellular processes.

   • Errors During DNA Replication: Mistakes made while copying DNA.

   • Errors in DNA Repair: Failures in the enzymes that correct DNA mistakes.

2. Mutagens: External factors that cause mutations.

   • Radiation:

     • UV Radiation

     • X-Rays

   • Chemicals:

     • Cigarette smoke

     • Benzoyl peroxide

     • Nitrate and nitrite preservatives

     • Overcooked charred food (barbecuing)

   • Infectious Agents:

     • Human papillomavirus (HPV)

     • Helicobacter pylori

Types of Mutations

1. Gene Mutations: Changes to the DNA sequence that can alter the amino acid sequence of a protein.

   • Point Mutations:

     • Substitution: One base pair is replaced by another, which can result in a different amino acid in the protein.

   • Frameshift Mutations:

     • Insertion: Addition of one or more base pairs, shifting the reading frame.

     • Deletion: Removal of one or more base pairs, shifting the reading frame.

2. Chromosome Mutations: Changes to whole chromosomes or large segments.

   • Types:

     • Deletions

     • Duplications

     • Inversions

     • Translocations

   • Human Karyotype: A visual representation of all chromosomes in a cell, used to detect chromosomal mutations and abnormalities.

Impact of Mutations

Genetic Variation: Mutations are the primary source of genetic variation within a species.

• Natural Selection: Mutations that enhance survival and reproduction can be selected for by environmental conditions, driving evolution.

• Adaptive Mutations: Beneficial mutations can provide a selective advantage in changing environments.

• Neutral Mutations: Have no immediate impact on fitness but can accumulate over time.

• Harmful Mutations: Can reduce an organism’s fitness and may be selected against.