Functional organization of the Human Genome
The human genome comprises an estimated 20,500 "genes",
which can be divided into functional categories as
above. Only about 20% of the transcripts are responsible
for biochemical functions, loosely enzymes and
other proteins. Approximately a quarter of the
genome is responsbile for maintenance of the genome
itself, including polymerases, ligases,
helicases, etc. as discussed under DNA
replication, transcription and control
of transcription and translation Another
21% are responsible for signal
transduction, for example relaying
information about the extracellular environment across
the cell membrane to the cell nucleus, so as to produce
the appropriate response by change in gene
expression.The function of more than a third of the
genome is at present unknown. Inference of the
function of this portion of the genome proceeds by
identification of sequence motifs and comparison with
homologous genes in other creatures.
Figure © 2012 TA Brown, Introduction to Genetics (1st ed.); additional text © 2012 by Steven M. Carr