Bacteria and Archaea

Page
3

Bacteria Evolve Rapidly in Response to Environmental Conditions

EXPERIMENT

RESULTS

Daily serial transfer

0.1 mL

(population sample)

Old tube

(discarded

after

transfer)

New tube

(9.9 mL

growth

medium)

Fitness relative

to ancestor

Generation

0

5,000

10,000

15,000

20,000

1.0

1.2

1.4

1.6

1.8

Slide 18

Prokaryotes have considerable genetic variation.

Three factors contribute to this genetic diversity:

Rapid reproduction

Mutation

Genetic recombination

Concept 27.2: Rapid reproduction, mutation, and genetic recombination promote genetic diversity in prokaryotes

Slide 19

Rapid Reproduction and Mutation

Prokaryotes reproduce by binary fission, and offspring cells are generally identical.

Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population.

High diversity from mutations allows for rapid evolution.

Slide 20

Genetic Recombination

Prokaryotic DNA from different individuals can be brought together by transformation, transduction, and conjugation.

A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation.

Transduction is the movement of genes between bacteria by bacteriophages (viruses that infect bacteria)

Slide 21

Transduction

Recombinant cell

Bacteria Recipient

Cell

A+

B–

B–

A+

A–

Recombination

A+

Bacteria Donor

Cell

A+

B+

A+

B+

Phage virus DNA

Slide 22

Conjugation and Plasmids

Conjugation is the process where genetic material is transferred between bacterial cells.

Sex pili allow cells to connect and pull together for DNA transfer.

A piece of DNA called the F factor is required for the production of sex pili.

The F factor can exist as a separate plasmid or as DNA within the bacterial chromosome and is transferable during conjugation.

Slide 23

Conjugation

Sex pilus

1 µm

Slide 24

Conjugation

F plasmid

F+ cell

F– cell

Mating

bridge

Bacterial chromosome

Bacterial

chromosome

(a) Conjugation and transfer of an F plasmid

F+ cell

F+ cell

F– cell

(b) Conjugation and transfer of part of an Hfr bacterial chromosome