The ability to perform this transfer is conferred by a set of genes which are called F for fertility. These genes can exist on a small, circular piece of DNA that replicates independently from the bacterial chromosome, or they can be integrated into the chromosome. The bacterium containing this gene (often parochially called the "male" bacterium) shoots a grappling hook (called a pilus) out to sieze a neighbouring bacterium. The two cells then are drawn together, and the grappling hook forms a channel through whch DNA is transferred. This process is called bacterial conjugation.
Microbial biologists have learned to take advantage of this phenomenon. When you were studying mendelian genetics, you could often analyse the function of a gene by looking at how it related to its allele pair: is the allele you are looking at recessive or dominant? In a haploid organism like the prokaryote, this analysis is impossible. However, pseudo-diploid (meridiploid) genetics can be conducted by putting various alleles of a gene of interest on the F element, along with the fertility genes. That way the genes can be transferred to another bacterium, which might already contain different alleles of those genes. The effect of the two alleles on each other can then be examined.
There are three manifestations of the fertility factor:
|Hfr||The F element has become integrated into the
When conjugation occurs, the F genes start travelling across the pilus,
dragging the rest of the genome behind it. Eventually, the pilus breaks,
so most often the entire genome is not transferred. The bacterial genome can
be measured in minutes from the origin of transfer: The amount of time it takes
for a particular gene to be transferred from one bacterium
to another indicates how far it is from the origin of replication.
|F'||Also called the F' episome. This is a small circular piece of DNA
that contains the fertility genes and a few other genes. These other
genes are transferred very efficiently from one bacterium to the next
because the length of the transferred DNA is short enough that it can
move across the breach before the pilus breaks.
|F||This is a small circular piece of DNA carrying only the fertility genes.|