Guide to the Human Genome

DNA structure

  • DNA strands pair up in an antiparallel fashion
  • Read and replicated 5’→3’
  • Sugar phosphate backbone (deoxyribose)
  • A + T, C + G
  • DNA strand associates with proteins (including histones) – wound into chromosomes

DNA replications

  • DNA can be damaged during replication
  • When repair mechanisms are defected, disease occurs

Cell cycle

  • G1 → S → G2 → M
  • DNA synthesis occurs during S phase

Mitosis

  • One diploid parent cell becomes 2 identical diploid daughter cells

Meiosis

  • One diploid parent cell becomes 4 haploid daughter cells
  • Crossing over occurs
  • Gamete formation

Transcription and translocation

  1. DNA transcribed into pre-mRNA
  1. Pre-mRNA-spliced to mRNA (introns removed)
  1. mRNA translated into protein
      • 3 bases encode 1 amino acid or stop codon
  1. Protein is modified and moved around the cell

RNA

  • Single stranded
  • Ribose sugar backbone
  • U replaces T

Variation in the human genome

Sequence variations within a gene

  • Changes in promoter sequence
  • Changes in exon sequence

Sequence changes in DNA between genes

  • SNPs: Single Nucleotide Polymorphisms
    • Affect gene function, some effects may make you more prone to disease e.g. by affecting transcription (alter promoter)
    • Most have no effect
  • CVNs (copy number variation): extra/missing stretches of DNA; deletions or duplications
    • Number of copies of a particular gene varies from one individual to the next