Bacterial colonies growing on Petri dish

Evidence for recombination in bacteria

Evidence for the

requirement of contact

in conjugation

Bacterial conjugation

An F+ x F- mating

Hfr bacteria and

chromosome mapping

Mapping by interrupted

mating

aziR = resistant to

sodium azide

tonR = resistant to

bacteriophage T1

tonR

Figure 6.9

Genetic evidence for a circular chromosome

Evidence for circular map

F’ and the generation

of partial diploids

(merozygotes)

R plasmids

Transformation

Determining gene order by co-transformation

Bacteriophage genetics

Plaques of bacteriophage T4 in E. coli

Life cycle of bacteriophage T4

Generalized transduction

Order of genes from generalized transduction data

leu+ + aziR = 50%

leu+ + thr+ = 2%

thr+ + leu+ = 3%

thr+ + aziR = 0%

Life cycle of a temperate phage

Specialized

transduction by

λ

Plaques of bacteriophage T2 in E. coli

Mapping Bacteriophage genes

Phage = T2

Genes=

h+, h host range

h+ can lyse B not B/2

h can lyse both

r+, r rapid lysis mutant

r+ small plaques

r large plaques

Looking for recombination

Mapping Bacteriophage genes

Recombinant phages growing on B/B2 lawn

Distance = number of recombinant plaques

total number of plaques

h r+ X h+ r

parentals

h r+

h+ r

recombinants

h r

h+ r+

Fine structure analysis of bacteriophage genes

T4 rII mutants

Seymour Benzer

Two questions to be answered:

1. Are all rII mutations in the same gene?

Complementation testing

2. Are mutations in the same gene capable

of recombination?

Learning more about phage genetics

rII mutants of bacteriophage T4

wild-type phage - produce small plaques in both E. coli strain B and E. coli

strain K12

rII mutants – produce large plaques and are able to grow on E. coli strain B

but not on E. coli strain K12(λ) K12(λ)

WT rII on B rII on K

Complementation testing

A geneticist is working with a new bacteriophage, Y3, the infects

E. coli. He isolated eight mutations that fail to produce plaques in

strain K. To determine if these are mutations of the same functional

gene, he infects K cells with paired combinations of his mutants to

see if plaques are formed. Here are the results. + = plaques , - no

plaques.

Mutant 1 2 3 4 5 6 7 8

1

2 +

3 + +

4 + - +

5 - + + +

6 - + + + -

7 + - + - + +

8 - + + + - - +

To how many functional genes (cistrons) do these mutations belong?

Which mutations belong to each functional gene?

How recombination within a gene could generate wild-type

Protocol for recombination studies

Benzer’s method for identifying recombinants of two rII mutants of T4.

How deletions are used for rapid mapping

Deletions for rapid mapping of point

mutations to a region of the chromosome