what is vertical gene inheritance?
asexual reproduction via cell division
what are the three types of horizontal gene transfer?
- conjugation
- transduction
- transformation
what is horizontal gene transfer?
organism acquires genes directly from another cell and incorporates them into its genome
- responsible for the spread of fitness-enhancing traits, including antibiotic resistance
- provides an awesome mechanism for ongoing adaptive evolution
what is conjugation?
DNA transfer through cell-to-cell contact mediated by a mobile genetic element such as a plasmid
what is conjugation mediated by?
a mobile genetic element like a plasmid
what is transduction?
DNA transfer mediated by a bacteriophage
what is transformation?
uptake of naked DNA into a competent recipient cell
what is the direction of transfer?
unidirectional, from donor to recipient
how much of the genome is transferred?
only part of the genome
what form is the DNA in when it is transferred?
in a linear form that cannot replicate autonomously
how are genes stably inherited?
they must be recombined into the recipient chromosome
what was the basis of Lederberg’s experiment?
- represented the first use of conditional mutants to select against the parental type
- the mutants were double mutants so reversion artifacts were avoided
- the prototrophic recovery technique had enormous sensitivity
what was the Davis U-tube experiment?
Two strains are added into a U-tube, seperated by a fine filter
It was mixed for several hours and then the solutions from each side of the U-tube were plated
what were the results of the Davis U-tube experiment?
no recombinants
what did the Davis U-tube experiment show?
that physical contact is required for genetic recombination
how does an F factor transfer?
F factor can transfer from F+ cell to F- cell at high frequency by rolling circle mechanism
F- becomes F+ while F+ remains F+
F+ does not mate with F+ (surface exclusion)
what is the donor F plasmid?
Donor F+ (male)
what is the recipient F plasmid?
Recipient F- (female)
how are Hfr strains formed?
by homologous recombination between identical copies of an insertion sequence or transposon present on F and on the chromosome
what are the structural features of the F plasmid?
~100.00 Kb
hok/sok
pif
oriT
what is the disrupted mating experiment?
added plasmids to a blended and blended them at different intervals
what are the conclusions from the interrupted mating experiment?
- each donor allele first appears in recipient at a specific time after mating begins
- donor alleles appear in a specific sequence
- the maximal yield of cells containing a specific donor marker is lower for the donor markers that enter later
- Hfr chromosome is transferred in a linear fashion, beginning a specific origin. The further from O, the later a gene will be transferred and the more likely the transfer process will be interrupted before the gene is transferred.
how many crossovers is required to incorporate transferred DNA?
An even number of crossovers
What is the purpose of High Resolution Mapping by recombination Frequency?
to determine the distance between markers (interrupted mating will determine the order of markers)
