Understanding DNA, Chromosomes, and Genes

Oct 3, 2024

Lecture Notes on DNA, Chromosomes, Genes, and Genomes

Introduction

  • Overview of DNA, chromosomes, genes, and genomes.
  • Goal: Understand definitions and relationships between these terms.

DNA (Deoxyribonucleic Acid)

  • Chemical structure of genetic material.
  • Polymer made of repeating units.
  • Double helix structure (two strands coiled together).
  • Length: Unraveled DNA from a single cell = over 2 meters.
  • Organized into 46 chromosomes to fit inside the nucleus.

Chromosomes

  • Chromosome Structure:
    • 46 different sections (chromosomes) in human cells.
    • Each chromosome is a tight coil.
    • Only 23 different types (two of each type from parents).
  • Chromosome Pairs:
    • Two chromosome 1s, two chromosome 2s, etc. up to chromosome 23.
    • 23rd pair are sex chromosomes:
      • Women: XX (two X chromosomes)
      • Men: XY (one X and one Y chromosome)
  • Common Misconception:
    • Chromosomes are often depicted in an X shape, which only occurs before cell division (mitosis/meiosis).
    • In resting cells, chromosomes appear more dispersed.

Genes

  • Definition:
    • Small sections of DNA that code for specific proteins.
  • Function:
    • Gene = code for a sequence of amino acids which form proteins.
    • 20 different amino acids can combine in numerous ways to create thousands of proteins.
  • Role of DNA in Cell Type Determination:
    • Example: Red blood cells need hemoglobin for oxygen transport; muscle cells need proteins for contraction.

Genome

  • Definition:
    • Entire set of genetic material in an organism.
  • Comparative Genomics:
    • Individuals have different genomes, but family members share similarities.
    • Identical twins share the same genome.
  • Human Genome:
    • Complete mapping of the human genetic code.
    • Enables identification of genes linked to diseases (inherited diseases vs. risk-increasing genes).
    • Example: BRCA genes increase breast cancer risk.
  • Applications of Genome Analysis:
    • Help doctors choose effective treatments.
    • Trace migration patterns of ancestors and human population separations (e.g., migration from Africa).

Conclusion

  • This lecture covered the basics of DNA, chromosomes, genes, and genomes.
  • Next topic: Alleles, genotypes, phenotypes, and the concepts of homozygous vs. heterozygous.