A passage from such a book in English might look like this:. Even in a familiar language it is difficult to pick out the meaning of the passage: The quick brown fox jumped over the lazy dog. The dog lay quietly dreaming of dinner. And the genome is "written" in a far less familiar language, multiplying the difficulties involved in reading it. So sequencing the genome doesn't immediately lay open the genetic secrets of an entire species.
Even with a rough draft of the human genome sequence in hand, much work remains to be done. Scientists still have to translate those strings of letters into an understanding of how the genome works: what the various genes that make up the genome do, how different genes are related, and how the various parts of the genome are coordinated.
That is, they have to figure out what those letters of the genome sequence mean. At the very least, the genome sequence will represent a valuable shortcut, helping scientists find genes much more easily and quickly. A genome sequence does contain some clues about where genes are, even though scientists are just learning to interpret these clues.
Finally, genes account for less than 25 percent of the DNA in the genome, and so knowing the entire genome sequence will help scientists study the parts of the genome outside the genes. The quick answer to this question is: in pieces.
The whole genome can't be sequenced all at once because available methods of DNA sequencing can only handle short stretches of DNA at a time. So instead, scientists must break the genome into small pieces, sequence the pieces, and then reassemble them in the proper order to arrive at the sequence of the whole genome. Much of the work involved in sequencing lies in putting together this giant biological jigsaw puzzle.
There are two approaches to the task of cutting up the genome and putting it back together again. Image credit: Genome Research Limited. After the sections of DNA sequence have been assembled into a complete genome sequence we need to identify where the genes and key features are, but how do we do this?
The Human Genome Project, which began officially in , was the largest international collaboration ever undertaken in biology and involved thousands of scientists. Each genome contains all of the information needed to build that organism and allow it to grow and develop. If you have any other comments or suggestions, please let us know at comment yourgenome. CrossRef Medline Google Scholar. Cantatore, P. Clayton, D. Medline Google Scholar. Gilbert, W. Nature : , doi: Gissi, C. Heredity : — Landweber, L.
Why genomes in pieces? Science : — Lavrov, D. Lukes, J. Cell 1 : — Lynch, M. Google Scholar. Marande, W. Science : , doi: Podsiadlowski, L. Pont-Kingdon, G.
Nature : — Rand, D. CrossRef Google Scholar. PLoS Biol. Shao, R. Genome Res. Smith, D. Snyder, M. Tsaousis, A. Voigt, O. BMC Genomics 9 : , doi: Conventional sequencing methods read DNA in chunks of only a few hundred base pairs at a time, and researchers reassemble these stretches like puzzle pieces. The larger pieces are much easier to put together, because they are more likely to contain sequences that overlap.
T2T-CHM13 is not the last word on the human genome, however. The T2T team had trouble resolving a few regions on the chromosomes, and estimates that about 0. There are no gaps, but Miga says quality-control checks have proved difficult in those areas. And the sperm cell that formed the hydatidiform mole carried an X chromosome, so the researchers have not yet sequenced a Y chromosome, which typically triggers male biological development.
But the T2T Consortium has teamed up with a group called the Human Pangenome Reference Consortium, which aims over the next 3 years to sequence more than genomes from people all over the world. Miga says that the teams will be able to use T2T-CHM13 as a reference to understand which parts of the genome tend to differ between individuals. Miga expects that genetics researchers will quickly find out whether any of the newly sequenced areas and possible genes are associated with human diseases.
She hopes that future human genome sequences will cover everything, including the newly sequenced sections — not just the parts that are easy to read.
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