Cytologic observations and genetic studies indicate something like sexual reproduction, involving the fusion
Sexual reproduction in bacteria is called two different cells and a transfer of hereditary factors occurs in bacteria although Sexual reproduction in bacteria is called. Genetic recombination occurs in those bacteria that have been carefully studied and presumably occurs in other species as well. One of the most intensively studied species of bacteria, Escherichia coli has been shown to have sex-some act as males and transfer genetic information by direct contact with females.
The usual vegetative bacterial cells are Sexual reproduction in bacteria is called and in sexual reproduction part or all of the chromosome passes from the male cell to the female cell, yielding a cell, i. Crossing over then occurs between the female chromosome and the male chromosome or fragment, followed by a process of segregation that yields haploid progeny cells. The genetic transfer in bacteria also occurs by transformation, in which the DNA molecule of the donor cell, when liberated by its disintegration, is taken up by another recipient cell and its offspring inherit some characters of the donor cell.
When different strains of bacteria are found in a mixed state either in culture or in nature, some of the resultant offspring possess a combination of characters of the parent strains. This phenomenon is known as recombination. The phenomenon of transformation was first recorded by Griffith Avery, Macleod and McCarty demonstrated Sexual reproduction in bacteria is called the transforming principle being DNA in the sequence of events in bacterial transformation.
The lines of inquiry that led to an understanding of the chemical nature of genetic material arose from a study of the pestilent organism Diplococcus pneumoniae. This bacterium causes pneumonia in males. InFrederick Griffith found that there are two strains of D. When injected into A only capsulated smooth cells virulent produced the disease, but not the non-virulent rough cells B.
On the other hand when the heat killed capsulated virulent smooth cells were mixed with non-virulent rough cells D Sexual reproduction in bacteria is called then were injected in the mice the disease was produced.
This shows that some factors from the dead capsulated smooth cells, converted
Sexual reproduction in bacteria is called living non-virulent rough cells into living smooth capsulated virulent cells, see fig.
They found that the DNA isolated from the heat killed smooth cells, when added to rough cells changed their surface character from rough to smooth, and also made them virulent. By this experiment, this was shown that DNA was the genetic material responsible for inducing the smooth character of the cells and their property of virulence in mice.
Their experiment proved that bacterial transformation involves transfer of a part of DNA from the dead bacterium i. A bacteriophage T 2 virus infects the bacterium Escherichia coli. After infection, the virus multiplies and T 2 phages are released with the lysis of the bacterial cells. As we know, the T 2 phage contains both DNA and proteins. Now the question arises, which of the two has the information to programme for the multiplication of more viral particles.
To solve this problem Hershey and Chase devised an experiment with two different preparations of T 2 phage. In one preparation they made protein part radioactive and in the other preparation the DNA was made radioactive. Thereafter a culture of E. Immediately after infection and before lysis of bacteria the E. With the result the heavier pellets of bacterial cells were settled down in the bottom of tube.
The lighter viral particles and those particles which did not enter the bacterial cells were found in the supernatant. On the other hand when T 2 phage with radioactive protein was used, the bacterial pellet had very little radioactivity and most of the radioactivity was found in supernatant. However, in some viruses e.
Hershey and Chase conducted two experiments. In one experiment E. In these experiments E. When these phages were used to infect new E. Whereas the bacteria infected with P 32 labelled phages had shown the reverse condition. Thus it can be said that when T 2 phage Sexual reproduction in bacteria is called the bacterial cell, its protein capsid remains outside Sexual reproduction in bacteria is called the bacterial cell but its DNA enters the cytoplasm the bacterium.
the infected cells of bacteria get lysed, new complete viral particles T
Sexual reproduction in bacteria is called phages are formed. This shows
Sexual reproduction in bacteria is called DNA is genetic Sexual reproduction in bacteria is called, see fig. The genetic transfer in bacteria is achieved by a process known as transduction. Thus the host acquires a new genotype.
Transduction has been demonstrated in many bacteria. In this process, the DNA molecule that carries the hereditary characters of the donor bacterium is being transferred to the recipient cell through the agency of the phage particle. In this process very few closely linked characters can be transferred by each particle. Thus the bacteriophage brings about genetic changes in those bacteria which survive the phage attack.
When a bacterial cell is being infected with a temperate virus either lytic-cycle or lysogeny starts. Thereafter, host DNA breaks down into small fragments along with multiplication of virus.
When bacteria lyse these particles along with normal virus particles Sexual reproduction in bacteria is called released. A few bacteria are infected with transducing particles, transduction takes place and the DNA of virus particles undergo genetic recombinations with the bacterial DNA. Wollman and Jacob have described conjugation in which two bacteria lie side by side for as much as half an hour.
During this period of time a portion of genetic material is slowly passed from one bacterium which is designated as a male to a recipient designated as a female. This was established that the male material entered the female in a linear series. The genetic recombination between donor and recipient cells takes place as follows: The Hfr DNA
Sexual reproduction in bacteria is called leaving a part in fragment to recipient Sexual reproduction in bacteria is called again reforms in circular manner.
In F strain genetic recombination takes place between donor fragment and recipient DNA. Gene transfer is a sequential process and a given Hfr strain always donates genes in a specific order. A single stranded donor DNA F factor is integrated in the host chromosome with the help of nuclease enzyme, see figs. In bacterial conjugation the transfer of genetic material DNA takes place by cell to cell contact of donor and recipient cells.
During the process of conjugation large portion of the genome is transferred, while in transformation and transduction only small fragment of DNA is transferred. The process of conjugation was discovered by Lederberg and Tatum in a single strain of Escherichia coli.
Conjugation has also been demonstrated in Salmonella, Pseudomonas and
In conjugation one way transfer of genetic material takes place from donor to recipient strain. The donor and recipient strains are always determined genetically. Sex pilus has a hole of 2.
The circular DNA of H fr cells opens and replicates but during transfer, one strand Sexual reproduction in bacteria is called DNA is newly synthesized, whereas the other strand is derived Sexual reproduction in bacteria is called a pre-existing strand of H fr strain. After transfer of DNA both the cells are separated from each other. The H fr DNA after leaving apart its fragment to recipient cell again reforms in circular manner.
In F — strain genetic recombination takes place between donor fragment and recipient DNA. Gene transfer is a sequential process a given H fr strain always donates genes in a specific order. If F — and H fr strains
Sexual reproduction in bacteria is called allowed to mix in a suspension, different genes in a sequence of time are transferred from the genome of H fr to F — strain. Genes that enter early, always appear in larger percentage of the recombinations than do genes Sexual reproduction in bacteria is called enter late, see figs.
These recombinants are variable in their constitution and so also in their phenotypic expression. These recombinants are entirely new and different from their parents. You must be logged in to post a comment. Is Proteins a Polymer of Amino Acids? Leave a Reply Click here to cancel reply.