Biology Reference
In-Depth Information
Genome
3.2 Gb
mtDNA
16.5 kb
25%
75%
21%
Genic and
related
Extragenic
DNA
Unique/low
copy
2%
23%
54%
Coding and
regulatory
regions
Tandem
repeats
9%
45%
Interspersed
repeats
Non-coding
Repetitive DNA
Satellite
DNA
Micro-
satellite
Mini-
satellite
DNA
transposon
SINE
LINE
LTR
5%
1%
3%
13%
21%
8%
3%
Figure 2.4
The human genome can be classified into different types of DNA based on its structure
and function. (Based on Jasinska and Krzyzosiak [11])
one by the Public Consortium and one by the private organization Celera Genomics,
that covered 90% of the euchromatic DNA [4, 5]. This was followed by later versions
that described the sequence of 99% of the euchromatic DNA with an accuracy of
99.99% [3]. The first genomes were composites made up from sequence data from
different individuals; genomes of several individuals have now been decoded [6 - 10].
The genome can be divided into different categories of DNA based on the structure
and function of the sequence (Figure 2.4).
Coding and regulatory sequence
The regions of DNA that encode and regulate the synthesis of proteins are called
genes; at the latest estimate the human genome contains only 20 000 - 25 000 genes
and only around 1.5% of the genome is directly involved in encoding for pro-
teins [3 - 5]. Gene structure, sequence and activity are a focus of medical genetics
because of the interest in genetic defects and the expression of genes within cells.
Approximately 23.5% of the genome is classified as genic sequence, but does not
encode proteins. The non-coding genic sequence contains several elements that are
involved with the regulation of genes, including promoters, enhancers, repressors and
polyadenylation signals; the majority of gene-related DNA, around 23%, is made up
of introns, pseudogenes and gene fragments.
Extragenic DNA
Most of the genome, approximately 75%, is extragenic. Around 20% of the genome is
single copy DNA, which in most cases does not have any known function, although
some regions appear to be under evolutionary pressure and presumably play an
important, but as yet unknown, role [12].
