bacterial genetics
Summary
Bacterial genetics covers how bacteria store, express, and exchange genes: usually one circular chromosome plus optional plasmids. Variation comes from mutation and horizontal transfer (transformation, transduction, conjugation), not meiosis. Most testable: telling the three transfer routes apart.
Detail
Meaning: Bacteria are haploid prokaryotes with one main circular chromosome, and many carry plasmids, small circular DNA molecules that often hold genes such as antibiotic resistance. Cells divide by binary fission, so offspring are clones apart from mutation. New gene combinations come from horizontal transfer: transformation (uptake of free DNA), transduction (a bacteriophage carries bacterial DNA), and conjugation (DNA passes through a pilus from an F factor donor to a recipient). Genes are often grouped in operons such as lac and trp.
Equation: N = N₀ × 2ⁿ, where N is the cell number after n generations, N₀ is the starting number, and n is the number of divisions (all unitless).
On the MCAT: Expect passages on spreading antibiotic resistance, or a filter experiment: if transfer still occurs when a filter separates the cells, contact is not needed, which points to transformation or transduction rather than conjugation.
Common confusion: Conjugation is gene transfer, not reproduction: the cell number does not rise, and the donor keeps its own copy. Usually only part of the DNA moves, so an Hfr cell (F factor integrated in the chromosome) rarely makes the recipient F+.
Sources
- Campbell Biology
- Molecular Biology of the Gene
- Brock Biology of Microorganisms
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.