Sequence
The X chromosome and its genes belong to the best studied objects
in human genetics. This chromosome plays a central role in the
history of human genetics as many basic principles in the field
such as linkage, positional cloning, triplet expansion and gene
inactivation have been pioneered with its help. The finished
sequence of the X chromosome will be published this year by
an international consortium led by investigators from the
Sanger Centre at Hinxton, UK. It seems therefore appropriate
and timely to show this chromosome as representative of the
human genome sequence. The exhibit displays the 155 million
base pairs printed onto 748 square meter of paper, which will
cover the walls of a large meeting room at the International
Conference Centre in Munich.
Exhibition
The exhibit will provide a visual representation of the chromosome
in a text format and will expose the spectator to the full extent
of its genomic space. The distribution of transcriptional units
across the genome, the density of frequent variants, the extent of
the non-coding genome regions, and the occurrence of repetitive
sequences in the genome are visualized in a single view at the
molecular level. This may allow the recognition of patterns which
are difficult to realize at a smaller scale thus facilitating the
comprehension of some of the higher dimensions inherent to the mere
string of nucleotides.
Many authors of seminal papers on the genetics of the X chromosome
will be present at this year's ESHG meeting. In fact, every
participant of the meeting will have her or his own interests
with the X chromosome via the identification of its banding pattern
under the microscope, the diagnosis of X-linked disease phenotypes,
or via a research project concerning the mapping of genes located
on this chromosome. The exhibit may act as a projection space which
allows everybody to track previous experiences and provides an outlook
to future undertakings. The island-like nature of the coding regions,
the size and distribution of the transcriptional units, the extension
of intergenic regions, the sheer extent of repeat elements and the
evolutionary conserved regions, will be on display allowing a
visualisation of the entire X chromosome which is not possible
with the limitations of a small computer screen.
X for unknown
The name X was used by the German zoologist
Henking in 1891 to denote an unknown structure which he could
differentiate from the nucleolus. The X chromosome is unique in
its conservation among species, the epigenetic changes it undergos
because it stays largely unpaired, the modes of inheritance resulting
from this and the selection of genes acting in single dose. This
unique constellation will ensure that the X will continue to attract
the attention of geneticists, this way improving both our knowledge
and our perception of what is still unknown about this chromosome.
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