The Genome

• Genome


  The complete set of genes or genetic material present in a cell or organism
• Eukaryotic chromosome


  Can be sex chromosome or autosome
• Prokaryotic chromosome


  Typically circular, more gene-dense and much smaller
• Karyotype


  Number of chromosomes in a cell
• Ploidy


  The number of sets of chromosomes (2 = diploid)
• Aneuploidy


  Wrong number of chromosomes
• Mitochondrial genomes


  • Approx. 10-15kB
• Chloroplast genomes


  • Approx. 100-200kB
• Different types of chromosomes

  • Autosomal genes
  • Y-linked genes
  • X-linked genes
  • Mitochondrial genes
  • Genes of our microbiome
• Genome sizes can be represented in a diagram
• Genome sizes (log scale)

  • 100bp
  • 1Kb
  • 10Kb
  • 100Kb
  • 1Mb
  • 10Mb
  • 100Mb
  • 1Gb
  • 10Gb
  • 100Gb
  • 1Tb
• SARS-CoV-2


  30kB genome
• Giant viruses


  3MB genome
• Circoviridae


  1. 2Kb genome
• Prokaryotes


  • Generally compact, circular genomes
  • Genes arranged into operons
  • Plasmids as “optional extras”
• Eukaryotes


  • Typically large genome (up to 150Gb)
  • Organised into chromosomes (1 to 1600; usually 10-100)
  • Organelles can have genomes separate from the nuclear genome
• Encephalitozoon cuniculi has a genome of 2.9 MB
• Polychaos dubium has a genome of 670 Gb
• Paramecium has two types of cell nucleus
• How to find genes

  1. Predicted ORFs

  2. Homology

  3. CpG islands

  4. RNA sequencing (transcriptome)
• The current state of the genome has just over 3 billion base pairs (haploid)
• There are 875 gaps in the sequence, some substantial (e.g. centromeric heterochromatin)
• There is less than 1 error per 100Kb in the genome