AS/A-level Biology - Genetic Variation in Bacteria

• Through the process of natural selection, species change to adapt to their environment – essential for reproduction and continuation of a species, this is known as adaptation.
• This can happen in two ways:
  (1) Mutation – this is when one code in a DNA sequence is deleted, changed or added. 
  (2) Reproduction – Recombining existing DNA of two individuals.

• A way of seeing adaptation is by looking at antibiotic resistance in bacteria.

Do you remember conjugation in AS/A-level Biology?

• Conjugation is a way of transferring DNA to another bacterial cell. 
• It occurs in the following steps:

1. A thin projection from cell meets another cell and a conjugation tube is formed between one bacteria and the other.
2. Plasmids from the resistant bacteria are replicated and broken so that they are linear do that they can pass through the tube.
3. The new bacteria now has the DNA to be resistant to the antibiotic.
4. The amount of contact is kept to a minimum – just enough to pass on the DNA.

Types of transmission

• Horizontal where DNA is passed from one species to another through conjugation.
• Vertical where DNA is passed down generations through reproduction.

• Joshua Lenderberg was a medical student who tested DNA been passed to other bacterial cells.
• He gathered 2 strains of bacteria, strain one could not develop 2 amino acids which it needs to grow and strain two could not develop another 2 amino acids which it needs to grow.

• Both strains were growing in mediums which helped them survive.
• They were then added to a minimal medium (without any supplements).
• There was no growth on any of the mediums, this can be explained because they don’t have the ability to synthesise amino acids.
• The two strains were then mixed together and grown in a medium which contained supplements of all of the missing nutrients.
• They were then added to a medium with all of the supplements and a minimal medium.
• As expected, bacteria grew on the medium with all supplements because it contained everything they needed to survive.
• What was found was that a few, about one in 10 million divided and developed into a colony of cells.
• This suggests that DNA has been passed from both strains of bacteria so that it can synthesise both amino acids to be able to survive.

That's the end of the topic!

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Drafted by Bonnie (Biology)