1. Nucleic acids are the physical basis of heredity. The discovery of pathogenic and infectious prions did not shake this theory.

2. Genome refers to both the coding and noncoding sequences in a cell or virus. Microbial genomes not only display diversity among taxonomically different groups (bacteria, archaea, and eukaryotic microorganism) but also within the same species. The concept of pan-genome is thus born. It refers to all the genes in a species. Metagenomic studies on all the genetic materials in culturable and unculturable microorganisms progress very rapidly. They play an important role in our understanding and application of microorganisms.

3. Plasmids are extrachromosomal, self-replicating, cytoplasmic genetic factors. Transposons are DNA sequences on a chromosome or on a plasmid that can change positions.

4. The change in gene structure or DNA sequence (deletion, insertion, or substitution) that leads to genetic alteration is called mutation. This type of change in the DNA structure or sequence (premutation) does not always cause mutation. It can be cleared or corrected by the DNA repair system in the cell.

5. Conjugation is the transfer of genetic material via direct cell-cell contact. Transduction is genetic exchange mediated by virus. Transformation refers to the uptake of foreign DNA by competent cells. Together, they are the three ways of horizontal gene transfer in bacteria.

6. Yeast is a single-celled eukaryotic microorganism. It is a model system for the study of eukaryotic genetics. Cloning and expression vectors based on the 2 m plasmid in budding yeast have been extensively used.

7. High-quality and high-yield microbial strains can be generated by altering genetic and metabolic characteristics of microorganisms via mutagenesis, metabolic engineering, gene recombination, DNA shuffling, etc.