Genetics and Mutations

Key Concepts: Mutations dark blue

Definition: A permanent change within a DNA sequence pink

  • Affects genetic material yellow

  • Gene Mutation: A specific mutation within a gene region that codes for proteins

  • Can affect how a gene is expressed:

    • Affect the presence or absence of expression

    • Alter the protein structure leading to changes in function

Types of Mutations: purple

  • Germ Cell Mutations pink

    • Occurs in germ cells (sperm or eggs) yellow

    • Can be transmitted to future generations and form the basis of heredity

  • Somatic Cell Mutations pink

    • Occur in somatic (body) cells, like liver or skin cells

    • Cannot be inherited but can predispose daughter cells to mutations during cell division

Categories of Mutations

  • Mutations can also be classified as:

    1. Spontaneous Mutations

    • Arise from errors during biological processes like DNA replication

    • 1 mistake per approximately 1,000,000,000 nucleotides

    • Example: A nucleotide mismatch during DNA synthesis that isn't corrected by repair mechanisms

    1. Induced Mutations

    • Result of exposure to mutagens (agents that cause mutations)

    • Types of mutagens include:

      • Radiation (e.g., UV rays, X-rays).

      • Chemical agents (e.g., tobacco smoke, certain food preservatives).

      • Infectious agents (e.g., HPV, H. Pylori known for linking to cancer).

Specific Mutation Types

Point Mutations

  • zzdefinition: Change occurs at a single nucleotidety

    • Base Substitution: Replacement of one nucleotide with another.

      • May or may not alter amino acid sequence depending on codon position.

    • Example: Sickle Cell Anemia: A single base substitution that leads to altered amino acid in hemoglobin, affecting red blood cell shape and function.

Frameshift Mutations

  • Caused by insertion or deletion of nucleotides

  • Alters the reading frame for codon transcription and translation

  • Significant effects on protein structure and function include:

    • Introducing premature stop codons or alterations in the amino acid sequence

Implications of Mutations

Effects on Proteins

  • Mutations can lead to either:

    • Gain of Function: Enhanced protein function leading to increased activity.

    • Loss of Function: Reduced or abolished protein function.

Oncogenes and Tumor Suppressor Genes

  • Mutations in proto-oncogenes lead to oncogenes that enhance cell division, causing uncontrolled growth

    • Philadelphia chromosome in leukemia

  • Mutations in tumor suppressor genes: reduce their ability to inhibit cell cycle, leading to cancer development

    • BRCA1 and BRCA2 mutations are associated with breast and ovarian cancers

BRCA Gene and Cancer Risks

  • Mutations in BRCA1: lead to up to 72% increased risk for breast cancer and 44% for ovarian cancer

  • Real-world examples of BRCA mutations:

    • Christina Applegate had a lumpectomy followed by a double mastectomy and oophorectomy due to increased cancer risks.

    • Matthew Knowles, father of Beyoncé, also had a BRCA2 mutation linked to various cancers and underwent a mastectomy and lymphoidectomy to treat cancer.

The Role of p53

  • Known as the guardian of the genome, involved in:

    • Cell cycle arrest

    • DNA repair processes

    • Apoptosis (programmed cell death)

  • Mutations in p53 are prevalent in cancer, affecting approximately 50% of all cancer types, with varying incidence among specific cancers

    • e.g., 90% in ovarian cancer, 80% in lung cancer