Molecular Genetics

Nucleotide sequences of genomes are the ultimate maps of molecular chromosomes.

Facts

Numerous projects were undertaken to establish complete nucleotide sequence maps of genomes. The first organisms tackled were phages and viruses. The first free-living organism to have its genome completely sequence was H. influenzae.

 The next table compares the gene distributions of organisms selected from the above table. Data are from Human Genome News (July 2001).

Interpretations

• The nucleotide sequence is the map of the molecular chromosome with the highest possible resolution.
• Determination of the entire nucleotide sequences of free-living organisms is expensive and is usually conducted by large sequencing centers.
• The availability of the complete nucleotide sequence of an organism provides a ready source of probes for correlation of morphological or genetic chromosomes with the molecular chromosome.
• The sequences also contain all the information necessary to specify the complete organism.

Further information

• Up-to-date lists of completed and on-going genome projects are available.
• In September 2000, there were over 900 genomes finished or being sequenced. in the databases. Most were viruses (557), but over 100 were bacteria, 13 were archaea and 157 were eukaryotes.
• "Completely" sequenced often means "mostly" sequenced. Highly repetitive sequence regions, which are difficult to sort through are often omitted. The degree to which "completed" sequences are annotated also varies with the organism.
• Comparison of genome sequences reveals considerable synteny.

This is page 11233 of Molecular Genetics by Ulrich Melcher, © 1997, 1998, 2000-1, 2003