Chapter 8 b

Methods of Genetic Exchange in Bacteria

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Summary:

Four ways bacteria exchange genetic material

Transformation, Conjugation, Sexduction, Transduction

Transformation

In bacteria, the cells take-up DNA from the environment and integrate it into the chromosome, if homologous regions exist between the chromosomal DNA and the DNA taken up. See Figure 16.6.

How does it occur?

Transformation Mapping

You can map genes using transformation analysis.

One Method:

  1. Take strain A (e.g., his-, met-) and collect DNA (kill the cells).
  2. Take strain B (e.g., his+, met+), grow, treat with above, grow.
  3. Plate 2 above onto a plate with pen and on minimal medium.
  4. After a short wait, wash away the pen and plate onto complete medium.
  5. All survivors must have received at least one of the minus genes. (Mutants occur at a lower frequency than transformants.)

In general:

E.g., if 50 met+ his-, 50 met- his+, and 100 met- met-; then (50+50)/(50+50+100) =.5

 

Conjugation

Conjugation in bacteria is a one way transfer of genetic information.

The rule for mapping is again that genes that are close together tend to stay together more frequently than genes that are father apart. The resulting map looks like this: See Figures 16.16 and "How we got it" 16.12.

 

Sexduction

Sexduction (F-duction)

This has been used for mapping. What do you expect? CTSTFAS

 

Transduction

First Lysogeny:

Example:

Three point analysis:

You expect four different classes:

A+, B+, C+

A+, B-, C-

A+, B-, C+

A+, B+, C-

 Homework Set for Viruses

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