Part 3: DNA recombination

Homologous (genetic) recombination

genetic exchange between 2 sequences that are nearly identical (large sections of chromosome)

Nonhomolous end joining (NHEJ)

genetic exchange between 2 DNA seq that are broken ends with no sequence similarity

Site specific recombination

genetic exchange that occurs at a specific sequence

Chiasmata

physical crossover point in prophase 1 of meiosis

Germ line

meiosis creates ___ cells

Aneuploidy

improper chromosome segregation during meiosis can lead to ____

3’

in homologous recombination (in meiosis) the exonucleases work at a ds break and degrade less of which strand…

Holliday intermediates

this is formed when the invading 3’ end of a homolog migrates to the other strand generating a DNA structure with 2 crossovers in the form of branched structures termed…

holliday intermediate resolvases

cleave the holliday intermediate and generate either of two recombination products

strand invasion, branch migration, strand displacement

the order of events in homologous recombination in meiosis prophase

RecBCD

associated with a ds break and unwinds and degrades DNA, stops at the chi segment on the 3’ strand leading to more degradation of the 5’ end

RecA

loaded onto the growing 3’ end of DNA behind the chi sequenced, forms nucleoprotein filaments during homologous recombination (6 subunits per turn)

RuvC nuclease

cleaves the holliday intermediate

Related sequences

non homologous end joining does not require

Non replicating stage

NHEJ is used when dsDNA breaks are present during a stage of the cell cycle

Recombinases

enzymes that bind and cleave at specific sequences

Recombination site

specific sequences 20-200 bp in length

Cre recombinase

binds holliday intermediate at LoxP sites, has four identical subunits that recognize and promote recombination at a specific 34 bp sequence (loxP), system has been adapted to knock out genes in mice

Site specific recombination

results in precise DNA arrangements, through transient binding with a tyrosine-phosphate linkage

Inversion, deletion and insertion

the two outcomes of genomic rearrangements that are possible with site specific recombination

Simple transposon

insertion sequences that possess only sequence needed for transposition for the transposase

Complex transposons

have an added sequence beyond the sequence for transposition, eg antibiotic resistance

Transposase

makes staggered cuts at the target DNA site, which creates a place for the transposon to be inserted and then where replication with fill in the gaps

Direct transposition

transposon exits the original chromosome and inserts itself into new chromosome, the original chromosome seals back up and now lacks the transposon sequence

Replicative transposition

the entire transposon is replicated into the new chromosome leaving a copy behind in the original chromosome

Antibody diversity

this is generated by unique combinations of VJC DNA segments

Bone marrow stem cells

programmed DNA rearrangements occur in the that differentiate into mature antibody producing B lymphocytes

Site specific recombination

immunoglobulin gene rearrangement involves

Recombination signal sequence

RSS that is removed and degraded created temporary hair pins that are joined together in immunoglobulin gene rearrangement