Biology - Gene Mapping
Crossing over diagram 1
Crossing over diagram 2
_T. H. Morgan,_ a geneticist who discovered linkage, suggested that the
extent or frequency of recombination  which occurs between genes on the
same chromosome  can indicate the distance between them.
In Crossing over  _diagram 1_, genes B and I are linked because they
are on the same chromosome.
When crossing over occurred, Crossing over_ diagram 2_ B and I became
separated as do b and i.
The further apart on the chromosome the genes are, the more likely they
will be separated if breaking and recombination occur. The closer they are,
the less likely.
It is therefore possible to analyse breeding experiments (see below) to
find out if there are large percentages of recombinants (individuals with
new combinations of characteristics) which would suggest that the genes
must be relatively far apart. Smaller percentages would suggest the genes
are closer together. The percentage of offspring that show recombination is
called the cross over value or frequency.
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