Chapter 6: Genetic analysis and mapping in bacteria and bacteriophages

Question 1

Describe chromosomes in bactera

Answer 1

single, circular chromosome
haploid

Question 2

What are some components of plasmids?

Answer 2

-replicate independently
-conjugative
-nonconjugative

Question 3

What are the three genetic recombinations in bacteria?

Answer 3

conjugation
transformation
transduction

Question 4

What is conjugation?

Answer 4

Direct contact between the donor and recipient cell

Question 5

Describe the purpose, methods and results of Lederberg and Tatum experiment?

Answer 5

Purpose - To discover if genes can be shared among cells

methods -
1. two different cultures (Y-24 strain and Y-10)
2. the cultures had opposite mutations when grown in complete medium
3. The separate cultures had no growth in minimal medium (all auxotrophic)
4. When cultures were mixed and transferred to minimal medium, there was growth (prototropic)

results: the growth in the mixture of cells indicated that the colonies were exchanging genes

Question 6

Describe the purpose, methods and results of the bernard david experiment?

Answer 6

Purpose - to discover if genes are begin shared through direct contact (mechanism of conjugation)

methods -
1. similar to lederberg and tutum, three samples, one mixed and two separate… no growth in separate and growth in mixed…
2. used a U-shaped tube with a filter in the middle that was too small for bacteria cells to pass through, so the cells remained separated
3. No growth from the U-shaped tube,

results: indicates there must be direct contact between the actual cells to initiate gene exchange

Question 7

What is the cause of conjugation between cells?

Answer 7

-direct contact via pilus (sex pilus)
- tube that DNA is transferred from donor to recipient

Question 8

How is it determined which cell will have the pilus?

Answer 8

-if the cell possesses the F factor…. genes necessary for pilus

Question 9

Describe the process of forming an exconjugate

Answer 9

start with F+ and F- cells (F+ has f factor)

plasmid containing f factor is unwound, a single strand of dna is passed through the pilus connecting the two cells

complementary strands are synthesized within both cells

finished product: F+ and F+ (recipient now has f factor and is known as exconjugate)

Question 10

What is an episome?

Answer 10

any plasmid that can be incorporated into main chromosome (f factor)

f factor integration:
IS element on plasmid and main chromosome… recombination occurs between these two sites and plasmid is incorporated into main chromo