Question

Sex factor of bacteria is
A. RNA
B. Sex pili
C. F-factor
D. Chromosome replicon

Answer 1

Hint: Plasmids are the extrachromosomal DNA present in the bacterial cells. Fertility plasmids carry the genes required for the formation of a special type of pili involved in the process of conjugation. These genes are also present on the chromosomal DNA in some bacterial cells.

Complete answer:
Mostly, bacteria have circular DNA as their genetic material. To distinguish it from the plasmid DNA, the DNA of bacterial cells is also called chromosomal DNA. The part of the bacterial DNA that contains the origin of replication and serves as a unit for replication is called replicon. The origin of replication is the site on the DNA where the process of replication starts.

Bacteria also have some surface appendages such as pili. Pili are the hairlike appendages present on the surface of bacterial cells. These structures anchor the bacterial cells to one another or other surfaces. The elongated pili of the bacteria are called sex pili.

As the name suggests, sex pili are involved in genetic recombination in bacteria during which DNA is transmitted between the bacteria. One of the processes of genetic recombination in bacteria is conjugation.

During conjugation, two different bacterial cells establish physical contact via conjugation tube, and the genetic material is transferred from one to the other. Here, the donor bacterial cells are also called F+ cells while the recipients are F- cells.

The main difference between the F+ and F- cells is the presence of the F- factor in the F+ cells. The F-factor is also called the fertility factor or the sex factor. The F-factor can be present on the DNA of the bacterial chromosome or as the plasmid. Its presence is required for a bacterial cell to serve as a donor during conjugation. This is because the genes present on the F-factor code enzymes involved in the transfer of DNA.

F-factor also carries the genes that encode the sex pili. The sex pilus of the F+ cell forms a conjugation tube between the F+ and F- cells and thereby, make physical contact between them.

Hence, the correct answer is option (C).

Note: Mostly, bacteria reproduce asexually through binary fission. However, genetic recombination in bacteria occurs by transformation, transduction, and conjugation. Two bacterial cells do not come in contact with each other during transformation and transduction. However, sex pili establish contact between the bacterial cells during conjugation. The bacteria that lack the F-factor lack sex pili and cannot serve as a donor during conjugation.