Recombination, Hfr, Transduction

Where does site specific recombination occur? Recognized by? Catalyze?

At particular DNA sequences recognized by enzymes that recognize said DNA sequences and catalyze recombination with a specific recipient DNA

Can a good copy of a gene fix a bad copy of a gene?

Yes

What does homologous recombination (general recombination) occur?

Occurs between DNA sequences that are homologous- this is the two DNA sequences are nearly identical

What does homologous recombination require?

RecA

What is reciprocal crossover?

Receive hybrid strands and information is reciprocal because it has been shared between strands (double crossover)

What is a non-reciprocal crossover?

Information is not shared equally between two strands (single crossover). One strand is missing information and the only one strand is hybrid. A deletion event occurs

Can double reciprocal crossovers occur? What about a double non-reciprocal crossover?

Yes to both

What is intramolecular recombination?

It is a recombination event that can occur if enough sequence homology exists that results in a piece of DNA to loop out and results in a short and circular piece of DNA.

Is intramolecular recombination a common way for plasmids or phage DNA to integrate?

Yes

How can phages be excised out of bacterial DNA?

Through intramolecular recombination

What is recombination frequency? Is it fairly constant? What can exist?

It is the probability that recombination will occur at a site of DNA and is fairly constant. But hotspots can exist

What does increasing the amount of homology do?

Increase the chances for recombination

What does homology infer?

An evolutionary linkage

Why does speciation occur?

Because of recombination

The further apart the two DNA positions are the greater?

The probability that there will be a recombination event between them

What are DNA sequences that can be distinguished called?

Markers

What are recombinations frequencies directly proportional to?

Distance between two markers

What do genetic crosses often use?

Co-inheritance of markers to tell how close genes are to each other

What is co-inhertiance frequency inversely proportional to?

The distance between two DNA markers

If a drug resistant cassette is put in can you measure for this?

Yes as it is a marker

What is recombination mediated by?

RecA

What is RecAs job?

To pair homologous DNA segments together so they can exchange strands

What does RecA bind to? Are other proteins involved?

DNA (usually ssDNA) and yes

What happens once RecA binds to DNA?

More RecA monomers bind cooperatively (more than one RecA) to make a nuclei-protein filament

What does the nucleoprotein filament do? What is it like?

It looks for homology to pair with and recombine. Beads on a string

Do RecA proteins displace SSB proteins?

Yes they do

How can you stop RecA recombination?

Make a mutant of RecA (need to have RecA deficient conditions)

What can happen if you have a ssDNA and a ds plasmid?

RecA can bind ssDNA and can invade the ds plasmid to get a formation of a D loop

What can happen if you have dsDNA and a ss plasmid?

Can get strand exchange between dsDNA and ss plasmid as RecA will bind to the ss plasmid

Can a damaged plasmid be repaired by dsDNA through recombination? Do you get strand exchange?

Yes you can and yes

What does homologous recombination require?

Substantial DNA sequence homology between the donor and recipient DNA

Is recombination between any two sequences a low or high frequency event?

Low (doesn’t happen all the time)

What is required to identify a specific recombination site?

A genotypic or phenotypic selection/marker in vivo

What is co-inheritance of two genetic markers inversely proportional to?

The distance between them

When can homologous recombination be prevented?

In a recA mutant