Human Genetic Diversity and the Genome

Human Diversity and Genetics

  • Humans exhibit both similarities and differences, influenced by environment, experiences, and DNA.
  • DNA plays a role in determining appearance, traits, and health.

Genes and Traits

  • Thousands of genes exist in the human genome.
  • Sequence changes in individual genes can influence various traits:
    • Freckles
    • Lactose digestion
    • Earwax type (wet or dry)
    • Red-green color blindness
    • Eye color (e.g., blue eyes)
    • Taste perception (e.g., broccoli)
  • Individual genes can determine the likelihood of developing certain diseases:
    • Sickle cell anemia
    • Cystic fibrosis
    • Huntington's disease

Complex Traits and Multiple Genes

  • Multiple genes, along with environmental factors, influence complex traits:
    • Hair and skin color
    • Height
    • Weight
    • Blood pressure
    • Risk of type 2 diabetes
    • Depression
    • Autoimmune disorders

Genetic Similarity and Variation

  • Humans are 99.9% genetically identical.
  • The 0.1% variation accounts for significant diversity.

DNA Structure

  • DNA nucleotide composition:
    • Sugar and phosphate groups
    • Nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
  • Sugar and phosphate groups form the DNA backbone.
  • Bases determine the DNA sequence.
  • Base pairing:
    • A pairs with T (two hydrogen bonds)
    • G pairs with C (three hydrogen bonds)
  • Human genome contains approximately three billion base pairs.

DNA Organization and Packaging

  • Total DNA length in a cell: approximately two meters.
  • Cell size: approximately 10 micrometers.
  • DNA is coiled into a helix structure.
  • DNA is wrapped around histone proteins to form nucleosomes.
  • Nucleosomes are further wound and coiled for compaction.
  • During cell division, DNA is organized into 46 chromosomes (23 from each parent).
  • Chromosomes ensure accurate DNA separation during cell division.
  • Outside of cell division, DNA is decondensed for accessibility.

Gene Expression

  • The transcriptional machinery regulates the expression of approximately 20,000 genes.
  • Genes represent less than 2% of genomic DNA.
  • Genes encode proteins necessary for cell function.

Genetic Variation and Diversity

  • The 0.1% genetic variation corresponds to approximately 3,000,000 differences in the genome.
  • About 20,000 of these differences occur in protein-coding genes.
  • These differences are not evenly distributed across coding regions.

Variants and Polymorphisms

  • Differences in DNA sequence are called variants.
  • Single nucleotide variants (SNVs) affect a single sequence position.
  • Common SNVs occurring in more than 1% of the population are called single nucleotide polymorphisms (SNPs).
  • SNPs, deletions, duplications, and rearrangements contribute to human genetic diversity.

Questions and Implications

  • How does DNA determine our traits?
  • How can we understand gene function and variant effects?
  • What can DNA reveal about disease risk?
  • How can genomic information improve medical care?

Applying Genetics

  • Understanding genetics allows us to apply heritability and genetic variation concepts to human health and disease.