What is an F’ factor? What is a merodiploid and how can F’ factors lead to the creation of these bacterial strains? Describe one piece of evidence provided by the use of merodiploid strains that contributed to the genetic proof of the operon model of gene regulation.
The correct answer and explanation is:
An F’ factor (pronounced F-prime factor) is a type of plasmid found in bacteria that is derived from the F (fertility) factor. The F factor is a genetic element that allows bacteria to transfer DNA to another bacterium via conjugation. Sometimes, the F factor integrates into the bacterial chromosome, forming an Hfr (high frequency recombination) strain. Occasionally, when the F factor excises from the chromosome, it does so imprecisely and takes with it a small segment of chromosomal DNA. This excised plasmid carrying some bacterial genes is called an F’ factor.
A merodiploid is a bacterial strain that carries two copies of a certain region of the genome. One copy is on the chromosome and the other is on the F’ plasmid. This partial diploidy occurs because the F’ factor carries chromosomal genes, effectively duplicating those genes within the same bacterial cell. The presence of two copies allows the study of gene function and regulation by comparing the effects of mutations or regulatory changes on each copy.
F’ factors lead to the creation of merodiploids because during the excision from the bacterial chromosome, the F factor carries along adjacent chromosomal genes. When this F’ plasmid is transferred by conjugation to a recipient bacterium, the recipient ends up with two copies of those specific genes: the original chromosomal copy and the F’ plasmid copy.
One important piece of evidence from the use of merodiploid strains helped confirm the operon model of gene regulation proposed by François Jacob and Jacques Monod. The operon model suggested that genes could be regulated by repressor proteins binding to operator sites. Merodiploid strains carrying both wild-type and mutant alleles of the lac operon were used to demonstrate dominance relationships between mutations. For example, when a merodiploid had one copy with a normal operator and another with a mutated operator that could not bind the repressor, the normal operator was dominant. This showed that the operator functions as a cis-acting site controlling only adjacent genes, confirming that gene regulation occurs at the DNA level and is specific to particular gene segments. This genetic proof was crucial in establishing how bacteria regulate gene expression in response to environmental signals.