genetic variation of prokaryotes

• Prokaryotes reproduce asexually by binary fission.
• Despite asexual reproduction, prokaryotes exhibit a great deal of genetic diversity through mutation and genetic transfer.
• The genetic material can be transferred between bacteria through transformation, transduction and/or conjugation.
• 35S being detected in the remaining solution provided further evidence that the protective phage coat of proteins remains outside the cell after adsorption.
• This transfer of genetic material gives rise to genetic variation within a bacteria population.
• Organisms with sexual reproduction usually have higher genetic diversity due to the rearranging of existing alleles in new combinations during meiosis and fertilisation.
• Genetic variation in prokaryotes is mainly due to mutations and rapid reproduction.
• Bacteria reproduce asexually via a process called binary fission whereby one parental bacterial cell will divide to produce 2 genetically identical daughter bacterial cells.
• Binary fission is considered a type of vertical gene transfer.
• Although mutation rates during binary fission are low, the short generation time resulting in a high rate of bacteria reproduction allows any mutated DNA sequence to be propagated and accumulated quickly in a population.
• Genetic recombination occurs in bacteria.
• Genetic recombination in bacteria occurs mainly through these three ways: Transformation, Conjugation, and Transduction.
• The main drawback of binary fission is that there is no genetic recombination, which means that the whole population risks being potentially wiped out if there is a change in the environment in which the bacteria cannot survive in.
• Bacterial cells reproduce asexually by binary fission, which is preceded by replication of the bacterial chromosome that begins at a single origin of replication (Ori).
• Mutations that form during rapid reproduction can greatly increase genetic diversity in bacteria which have short generation/doubling times and large population sizes.
• Genetic recombination involves the combining of bacterial DNA from different sources or different bacterial cells, for example, from different strains of bacteria.
• Through binary fission, most of the bacteria in a colony are genetically identical to the parent cell.
• Genetic recombination is considered a type of horizontal gene transfer as the genetic material is transferred from one bacteria strain to another bacterial strain, and not passed down from the parental cell to its offspring.
• As a cell divides by binary fission, a septum (cross-wall) is formed to separate the daughter cells.
• The advantages of binary fission include only needing one parent to reproduce, rapid division resulting in a lot of daughter cells produced in a short time, and daughter cells being genetically identical to their parent cells (clones), which means that any selective advantages are also passed down to daughter cells.
• A single strand of the F plasmid, beginning at the origin of transfer, enters the F- recipient cell.
• The F factor, made up of 25 genes, can exist either as a plasmid or as a segment of DNA within the bacterial chromosome.
• Cells containing F plasmid are known as F+ cells.
• Conjugation begins with the donor cell making contact with the recipient cell.
• Temperate bacteriophages replicate through either the lytic or lysogenic reproductive cycle, causing lysis of host bacterium or the bacteriophage can incorporate its DNA into the bacterium’s DNA and become a non-infectious prophage.
• A sex pilus from the F+ cell initially joins the two cells and creates a cytoplasmic bridge between cells where the cytoplasms of both cells are momentarily in contact.
• The F pilus recognises and binds to specific receptor sites on the cell wall of the recipient cell.
• A cell containing the F factor is known as an F+ cell.
• The process of conjugation involves the transfer of genetic material between two bacterial cells (same or different species) that are temporarily joined.
• Cells lacking F plasmid are known as F- cells.
• Biology Department Catholic Junior College Figure 4: Generalised Transduction and Specialised Transduction.
• The F+ condition can be passed on if an F+ cell transfers an F plasmid to an F- cell, converting it into an F+ cell.
• These F+ cells function as DNA donors during conjugation.
• The presence of a special piece of DNA called the F factor enables a prokaryotic cell to form the sex pilus and donate DNA during conjugation.
• The F plasmid then becomes activated/mobilised for transfer when a plasmid-encoded endonuclease cleaves a single strand of the plasmid DNA at the origin of transfer (made up of a specific nucleotide sequence).
• These F- cells function as DNA recipients during conjugation.
• The F plasmid encodes for the production of the F pilus (sex pilus), a protein appendage that attaches the donor cell to the recipient cell.
• The sex pilus retracts and pulls the donor and recipient cells together.
• If the F factor exists in a plasmid, the plasmid is called an F plasmid.
• Conjugation is a mechanism of gene transfer that requires direct contact between donor and recipient cells.