Describe the impact of gene mutation on human health.

Types of Gene Mutations

Gene mutations can be broadly classified into several categories based on the scale of the alteration:

• Point Mutations: These involve changes to a single nucleotide base.
  • Substitutions: One base is replaced by another (e.g., A to G). These can be further categorized as silent (no change in amino acid), missense (change in amino acid), or nonsense (creation of a stop codon).
  • Insertions: Addition of one or more nucleotide bases.
  • Deletions: Removal of one or more nucleotide bases.
• Chromosomal Mutations: These involve larger-scale changes affecting entire chromosomes or large segments of DNA.
  • Deletions: Loss of a chromosomal segment.
  • Duplications: Repetition of a chromosomal segment.
  • Inversions: Reversal of a chromosomal segment.
  • Translocations: Transfer of a chromosomal segment to another chromosome.

Causes of Gene Mutations

Mutations can arise from various sources:

• Spontaneous Mutations: Errors during DNA replication, repair, or recombination.
• Induced Mutations: Caused by external factors:
  • Radiation: UV radiation, X-rays, gamma rays can damage DNA.
  • Chemical Mutagens: Certain chemicals can alter DNA structure (e.g., benzene, asbestos).
  • Viruses: Some viruses can insert their genetic material into the host genome, causing mutations.

Impact of Gene Mutations on Human Health

The impact of gene mutations varies greatly depending on the type of mutation, the gene affected, and the individual's genetic background. Here's a breakdown of some key impacts:

Single-Gene Disorders (Mendelian Disorders)

These are caused by mutations in a single gene and often follow predictable inheritance patterns (autosomal dominant, autosomal recessive, X-linked).

Disorder	Mutation Type	Inheritance Pattern	Symptoms
Cystic Fibrosis	Deletion in the CFTR gene	Autosomal Recessive	Thick mucus buildup in lungs and digestive system
Sickle Cell Anemia	Missense mutation in the HBB gene	Autosomal Recessive	Abnormally shaped red blood cells, leading to pain and organ damage
Huntington's Disease	CAG repeat expansion in the HTT gene	Autosomal Dominant	Progressive neurodegenerative disorder
Hemophilia	Various mutations in genes coding for clotting factors	X-linked Recessive	Impaired blood clotting

Chromosomal Disorders

These are caused by abnormalities in chromosome number or structure.

• Down Syndrome (Trisomy 21): Presence of an extra copy of chromosome 21, leading to intellectual disability and characteristic physical features.
• Turner Syndrome (Monosomy X): Females with only one X chromosome, resulting in short stature and infertility.
• Klinefelter Syndrome (XXY): Males with an extra X chromosome, leading to reduced fertility and other developmental issues.

Complex Diseases

Many common diseases, such as cancer, heart disease, and diabetes, are not caused by a single gene mutation but by a combination of genetic predisposition and environmental factors. Mutations in multiple genes can increase the risk of developing these diseases.

Cancer: Mutations in genes controlling cell growth and division (oncogenes and tumor suppressor genes) can lead to uncontrolled cell proliferation.

Germline vs. Somatic Mutations

Germline mutations occur in reproductive cells (sperm or egg) and can be passed on to offspring. Somatic mutations occur in non-reproductive cells and are not inherited but can contribute to diseases like cancer.