In this topic of IBDP Biology, we will learn about Genetic Variation in Bacteria.

• Bacteria are prokaryotic cells.
• When it comes to IBDP Biology,  they have no true nucleus.
• However, they do contain DNA, which has the same molecular structure as eukaryotic DNA.
• The mechanism of its replication is very similar to how it replicates in our cells.
• Bacteria reproduce asexually by binary fission.
• In most cases the DNA is replicated producing two identical strands.
• Therefore, the daughter cells are clones – they are genetically identical to each other and to the original parent cell.
• However, there is great genetic variety in bacteria, even within a species.

1. Vertical gene transmission - Mutations

• During DNA replication, errors may occur, resulting in a change to the genetic code.
• This is very rare, but its occurrence will be high in bacteria with massive populations.
• This results in a structural change to the protein that a gene codes for.
• In most cases, this structural change results in a non-functioning protein.
• Most proteins are enzymes, and control metabolic reactions.
• A non-functioning enzyme may result in a block in a pathway.
• This is normally fatal and results in cell death.
• Occasionally, the cell survives to pass on this allele.
• Sometimes, mutations cause only a slight change to the protein – neutral mutations.
• The bacteria reproduce, passing on the allele.
• However, if the environment changes, there is a chance that some neutral mutations may become advantageous.
• When it comes to IBDP Biology,  the frequency of the allele increases if it provides a survival advantage.

2. Horizontal gene transmission – Conjugation

• Bacteria tend to form colonies.
• They attach to one another due to slime capsules and pili, which are protein fibres extending from the cells.
• When it comes to IBDP Biology,  where cell membranes come in close contact, they may fuse, forming a conjugation tube between the two bacteria.
• Their cytoplasms meet and substances can pass freely between the two cells.
• Small portions of DNA can be passed from one cell to another.
• These often pass as plasmids – small loops of DNA separate from the main bacterial DNA loop.
• There is evidence that bacteria of different species can exchange DNA by conjugation.

That's the end of this topic.

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