What is sex factor?

The sex factor, also known as the F factor (fertility factor), is a plasmid found in bacteria, most notably E. coli, that allows a bacterium to produce a pilus and transfer DNA to another bacterium via conjugation. Bacteria possessing the F factor are designated F+ (F positive) and are referred to as "male" cells. Bacteria lacking the F factor are designated F- (F negative) and are considered "female" cells.

Here's a breakdown of key aspects:

• Nature: The F factor is a circular piece of DNA separate from the bacterial chromosome. It's a type of plasmid.

• Conjugation: The F factor carries genes that encode for the proteins needed for conjugation, the process of transferring genetic material between bacteria through direct contact. This includes the synthesis of the sex pilus.

• F+ and F- Cells:

  • F+ cells contain the F factor and can initiate conjugation.
  • F- cells do not contain the F factor and can receive DNA during conjugation.

• Hfr Cells: An F+ plasmid can integrate into the bacterial chromosome through recombination. Cells with the F factor integrated into their chromosome are called Hfr cells (High frequency of recombination). Hfr cells can transfer chromosomal genes to recipient cells during conjugation at a high frequency. The recipient rarely becomes F+ because the entire F factor is usually not transferred.

• F' (F prime) Plasmids: Sometimes, when an integrated F factor excises from the chromosome, it can take a piece of the bacterial chromosome with it. The resulting plasmid is called an F' plasmid. The F' plasmid carries the F factor plus some chromosomal DNA. When an F' cell conjugates with an F- cell, the recipient cell becomes F' and also receives the chromosomal DNA carried by the F' plasmid.

• Role in Horizontal Gene Transfer: The sex factor plays a crucial role in horizontal gene transfer, contributing to genetic diversity and the spread of antibiotic resistance among bacteria.