Biology 1000ALecture 6 notes
• The first genome sequence ever reported was that of the bacterium Haemophilus Influenzae,
using the whole-genome shotgun method, whereas the entire genome is broken into millions of
random, overlapping fragments
• Each fragment is then cloned and sequenced
• With technology and computer algorithms evolving, the DNAof all organisms can now be
• This research is supported with studies such as infectious diseases, cancer medicine, enzyme
• Once a genome has been sequenced, the next step is annotation, whereas important genes,
generally protein coding genes are identified.
• Using computer analysis, researchers identify protein-coding genes by finding the start codon in
a sequence (ATG), and examining a multiple of three nucleotides at a time until the stop
• This is much easier to identify in prokaryotic genomes, since their genetic sequences have no
introns (genes which do not code).
• The bacterial organism Carsonella ruddii is the organism with the smallest known genome
sequence (182 genes).
• The genomes of organisms in the Eukaryote domain vary the greatest in size. For example, the
genome sequence of yeast is about 0.4% of the human genome sequence.
• Genome sizes are measured in megabase (Mb*), which represents one million bases.
• Genes are packed less densely in eukaryotes than in prokaryotes.
• The human genome sequence contains about 3 billion genes
• Only about 20000 genes are protein-coding genes.
• The protein-coding sequences occupy less than 2% of the human genome.
• Introns- the non-coding spacers in genes occupy about 24% of the genome.
• More than 50% of the human genome consists of repeated sequences that have no function
• There are bioethical issues arising to genomic studies; that genetic information should be
• Most eukaryotes have two copies of each chromoso