Genetics: Genetic is the study of heredity and variation
- Heredity characteristic are encoded in DNA.
- Bacterial DNA is circular double-stranded DNA ; 100 micrometre or 1 mm long.
- Extrachromosomal genetic material: plasmid
- Besides chromosomal DNA, some bacteria may possess extrachromosomal DNA that is plasmid and episode.
- Plasmid
- Extrachromosomal DNA is situated in cytoplasm as a free state.
- It is Circular DNA
- It Replicate independently
- Episomes
- Extrachromosomal DNA integrated with chromosomal DNA of bacteria.
- Plasmid and episode are nonessential for the function of bacterium but may vary properties of drug resistance, toxigenicity, conjugation etc.
- Plasmid has the ability to transfer themselves to other bacterium,(both are same or other species) so plasmids are important vector in recombinant DNA technology/genetic engineering.
Bacterial variation
There is two types of bacterial variation: phenotyping and genotyping.
Phenotypic variation
Expression of various characters in a given environment by a bacterial cell is known as phenotyping variation.
Bacterial cell may exhibit different phenotyping appearance in different environmental condition.
Examples:
- Synthesis of flagella: salmonella typhi are flagellated bacilli but grown in phenol agar, flagella are not formed. This effect is reversed when cultured into broth.
- Synthesis of enzyme: E coli has gene for synthesis of enzyme beta-galactosidase, but actual synthesis takes place only when grown in medium containing lactose i.e. inducible enzyme.
- Inducible enzyme: enzyme which are synthesized only when induced by the substrate are called inducible enzyme.
- Constitutive enzyme
- These enzymes are synthesized irrespective of the presence or absence of substrate.
Genotypic variation
Genetic variation occurs in genetic material as DNA so that is stable heritable
Not influenced by the environment
Occurs by mutation or gene transfer
Mutation
The mutation is a natural spontaneous random heritable variation caused by a change in the nucleotide sequence of the DNA of the cells.
The mutation causes both phenotypic and genotypic.
Mutation frequency: 10-2 – 10-10.per bacterium per division
Read more about Type of Mutation…