Slide 1
Inheritance can move sideways
Bacteria inherit genetic material when cells divide, but can also acquire it from other sources. This is horizontal gene transfer.
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The distinction concerns the route of transmission. A sequence acquired from another cell can later be copied vertically into descendants, so horizontal transfer and ordinary inheritance can act in succession.
Slide 2
Take up environmental DNA
In transformation, a bacterium takes up deoxyribonucleic acid (DNA) from its surroundings. Inheritance requires this material to persist or join a replicating system.
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Not every bacterium is equally able to take up DNA under every condition. The physiological state called competence depends on species and regulation, limiting when this route is available.
Slide 3
Transfer through contact
Conjugation transfers DNA between cells through specialized contact machinery. Mobile DNA elements can carry the instructions that enable this transfer.
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Plasmids are DNA molecules that can replicate separately from the main chromosome. Some carry useful genes, but not every plasmid can transfer itself, and their maintenance can impose a cost on the host.
Slide 4
Viruses can carry bacterial DNA
Bacteriophages, viruses that infect bacteria, can sometimes move bacterial DNA between cells. This route is called transduction.
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DNA transfer does not ensure lasting expression. Incoming sequences may be degraded, fail to integrate or be poorly regulated in the recipient, so movement and successful functional acquisition are separate steps.
Slide 5
Genes can have different histories
Horizontal transfer allows a gene’s history to differ from the lineage of the cell carrying it. Evolutionary reconstruction must account for that possibility.
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Genes involved in new metabolic abilities can spread through these routes. Comparing several genes and their genomic surroundings helps distinguish shared ancestry from a later exchange of one particular stretch of DNA.
Sources
- Gene Transfer and Minimal Genome Size
NCBI Bookshelf
- DNA Replication
National Human Genome Research Institute
- Mutation
National Human Genome Research Institute