are unlinked if they are located on different chromosomes, or are far enough
apart on the same chromosome that they will assort independently. On the other
hand, genes are said to be linked if they are situated closely on the same
chromosome. Instead of assorting independently, linked genes are often inherited
can occur amongst any pair of genes on a chromosome. The amount of crossing
over is usually dependent on how close these genes are located to each other. It
is rarer for a pair of genes that are near each other to undergo crossing over. If crossing
over does not take place, the products we get are parental gametes. If crossing over does occur, then we get
recombinant gametes. The reduced recombination that occurs between genes that are
in proximity results in much lower frequencies for the recombinants.
Calculating recombination frequencies allows determination
of gene linkage. Recombination frequency is described as
the frequency of crossing over between genes during meiosis. Genes positioned
on different chromosomes assort independently, having a recombination frequency
of 50%, while linked genes will have recombination frequencies less than 50%.
Another use for recombination frequencies is to
build linkage maps, which are genetic
maps based on calculated recombination frequencies. Linking maps can demonstrate the order and
relative distances between linked loci and order of linked loci on a
chromosome. A pair of genes with
a larger recombination frequency are likely farther apart, while those with a
smaller recombination frequency are likely closer together.