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Sequence for Yourself
Part V: Assembly and Finishing
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Assembly of 500-Base Segments
Perhaps you noticed in the last section that the human
DNA incorporated in the vector is 4,000 base pairs long
and that the 500 bases of human DNA we can read has to be
adjacent to the vector DNA. So how do we read the rest of
the human DNA? The answer is by piecing together
overlapping sequences.
Because we have many overlapping pieces, we also have many
starting points for the 4,000-base sequences -- enough to
allow us to read every base.
Assembly of 150,000-Base Segments
With the help of computers, we assemble the 500-base
sequences into the 150,000-base segments from which they
were derived.
Rebuilding the Chromosomes
Finally, we determine the chromosome that the 150,000-base
segment belongs to as well as where along the chromosome it
belongs. We do this by looking for overlaps and by looking
for matches in banding between the segments and
chromosomes.
Using this approach -- called the "map-based shotgun
approach" -- we can sequence the entire genome. To learn
about the differences between this approach and the "whole
genome shotgun" approach, check out the links in our
Resources
section.
Final Notes
Although the job of piecing together overlapping fragments
sounds straightforward, the task is a challenging one. Many
gaps will need to be filled in, and there are areas where
sequences are repeated many times, making it almost
impossible to determine where some of the fragments
belong.
In this explanation, some of the descriptions of the
techniques used were simplified. Also, for each of the
processes described here, researchers can use a variety of
techniques to get the same results.
Watch the Program Here
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Our Genetic Future (A Survey)
Manipulating Genes: How Much is Too Much?
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Understanding Heredity
Explore a Stretch of Code
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Nature vs Nurture Revisited
Sequence for Yourself
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Journey into DNA |
Meet the Decoders
Resources
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