Human Genetic Diversity and Similarity

Introduction

• Humans worldwide share similarities and exhibit vast diversity.
• Differences arise from environmental factors, life experiences, and DNA.

Role of DNA

• DNA influences appearance, traits, and health.
• Thousands of genes in the human genome.
• Sequence changes in genes affect:
  • Physical traits (freckles, skin type, lactose digestion, earwax type, colorblindness, eye color, taste perception).
  • Health conditions (sickle cell anemia, cystic fibrosis, Huntington's disease).
• Multiple genes and environment affect complex traits (hair/skin color, height, weight, blood pressure) and disease risks (type 2 diabetes, depression, cancer, autoimmune disorders).

Genetic Similarity and Diversity

• Humans are 99.9% genetically identical.
• 0.1% genetic variation corresponds to about 3 million differences across the genome.
• About 20,000 of these differences are in protein-coding genes.

DNA Structure and Function

• DNA consists of nucleotides composed of sugar, phosphate, and nitrogenous bases (A, T, G, C).
• DNA structure:
  • Sugar-phosphate backbone forms long strands.
  • Bases pair (A-T with two hydrogen bonds, C-G with three).
• Human genome: ~3 billion base pairs.
• DNA is coiled into helix, wrapped around histones to form nucleosomes, further compacted to fit into cell nucleus.
• Cell division: DNA organized into 46 chromosomes (23 from each parent).

Genetic Variation

• DNA sequence differences are called variants, single-position changes are SNVs.
• Common SNVs (>1% population) are SNPs.
• Larger sequence changes (deletions, duplications, rearrangements) contribute to genetic diversity.

Implications of Genetic Studies

• Understanding DNA and genetic variants helps answer questions about:
  • Trait determination.
  • Gene functions and variant effects.
  • Disease risk assessment.
  • Genomic impact on medical care.
• Genetics enhances our understanding of heritability and variation within human health and disease.