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Mapping a gene is not difficult so long as one
understands some basic genetic terms and processes.
To begin with, linked genes are genes located very
near each other on the same chromosome. As crossing-over
occurs, strongly linked genes rarely separate from
each other whereas those loosely linked do. Using
probability data from thousands of heredity experiment,
geneticists can determine the likelihood of two
linked genes splitting apart. This creates a series
of sorts which can be mapped much like dates on
a timeline. On a chromosome map, genes aren’t separated
by distance, really, but by their linkage strength.
Crossing Over
Sequencing DNA is much more difficult. First, all
3 billion bases are divided into 100,000 groups,
each with approximately 40,000 bases (some groups
overlap). Then, each of the fragments is divided
again into 100 pieces with 400 bases each. The precise
order of the amino acids (adenine, guanine, cytosine,
and thymine) is then determined for each 400 base
sequence. This is done with a technique called electrophoresis
which reads each acid’s identity chemical one at
a time. The overlapped pieces (mentioned above)
allow the researchers to fully connect the two strands
correctly together to make longer chains.
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