Question

Hfr forms of bacteria are those which have
(a)No F factor
(b)F factor
(c)F factor fused with the main chromosome
(d)None of the above

Answer 1

Hint: Bacteria is a type of biological cell which constitutes prokaryotic organisms. It ranges in few micrometers in length and has numerous shapes that vary from round to spiral. They were the first to appear on earth.

Complete answer:
The bacteria having an F factor fused with the main chromosome forms Hfr bacteria. Hfr stands for high-frequency bacteria. High-frequency recombination bacteria are those which have sex plasmid attached to the main chromosome. They contain more affinity towards F negative bacterial cells. The bacteria contain an F factor integrated into the bacterial genome. It conjugates with other bacteria and tries to transfer a copy of the F factor and the entire portion of the chromosome to the recipient bacteria. It was described by Luca Cavalli-Sforza who was a population geneticist. The integration of the plasmid into the cell's chromosome is through homologous recombination and the conjugative plasmid which is capable of chromosome integration is known as an episome. Episome is a segment of DNA that occurs as a plasmid and integrated into the chromosome.

Additional Information: Hfr cell transfers the bacterial genome in portions. Besides integrating the F factor of Hfr cells initiate the conjugative transfer. It is without the bacterial chromosome. The rest of the bacterial genome is dragged because of the F factors of the inherent tendency to transfer itself during conjugation. Therefore unlike the normal condition, the entire DNA is transferred through the mating bridge. The recipient cell becomes F positive after conjugation whenever it receives an entire copy of F factor plasmid during atypical conjugation. F plasmid that integrates with the chromosomal DNA is known as an F-prime cell. It carries the part of chromosomal DNA with it and being excised from the chromosome. The plasmid which contains the part of chromosomal DNA that can be transferred to the recipient cell during the conjugation is known as the F-prime plasmid.
So, the correct answer is ‘F factor fused with the main chromosome'.

Note: There are about 5 million trillion strong bacteria and their cousins on earth. Bacterias are 3.5 billion years old. It was not easy to catch a glimpse of bacteria by humans until 1674 when Antoni van Leeuwenhoek spotted the newly invented microscope.