molecular genetics recombination

Site specific recombination

Involves specific DNA sequences

Somatic recombination

Recombination that occurs in nongerm cells (common for immune system)

Synapsed chromosomes

Chromosomes must synapse (pair) in order for chrisamta to form where crossing over occurs

Sister chromatid

Each of two identical copies of replicated chromosome

Bivalent

The structure containing all four chromatids at the start of meiosis

Synaptonemal complex

The morphological structure of synapsed chromosomes

Joint molecule

A pair of DNA duplexes that are connected together through a reciprocal exchange of genetic material

Double strand break (DSBR)

Model of recombination that is initiated by making a double stand break in one DNA duplex and is relevant for meiotic and mitotic homologous recombination

5’ end resection

Exonuclease action generates 3’ singe stranded ends that invade the other duplex

Single stranded invasion

When a single stand from one duplex displaces it’s counterpart in the other duplex

D loop

A branched structure created after single stranded invasion

Heteroduplex DNA

Strand exchange that generates a stretch of DNA consisting of one strand from each parent

Branch migration

The ability of an DNA strand partially paired with its complement in a duplex to extend its pairing by displacing by the resident stand with which it is homologous

Steps in Holliday junctions

1.) First double strand break

2.) Each broken strand gets chewed back

3.) Strand invasion

4.) Second end capture synthesis

5.) Resolution

Resolution

The process where special enzymes called resolvases, cut a Holliday junction to separate the two DNA molecules linked by it

Mismatch (gap) repair

Heteroduplex DNA generates nonrepciprocal recombinant products called gene conversions

Gene conversions

Recombinant products generated from mismatch repair

BIR results

Initiated by one ended double strand break and at repeated sequences can result in translocations

Axial element

A protienaceous structure around which the chromosomes condense at the start of synapsis

Lateral element

A structure in the synaptonemal complex that forms when a pair of aister chromatids condenses on to an axial element

Central element

A structure that lies in the middle of the synaptonemal complex along which the lateral elements of homologous chromosomes align

Recombinant nodules (nodes)

Dense objects present on the synaptonemal complex; they represent protein complexes in crossing over

Recombinase

Enzyme that catalyzes site specific recombination

Core sequence

The segment of DNA that is common to the attachment sites on both the phage lambda and bacterial genomes

Phage

Is excised from the chromosome by recombination between the sites of the linear prophage

Integrases

Related to topoisomerases and the recombination reaction resembles topoisomerase action except that nicked strands from different duplexes are sealed together

Mitotic homologous recombination

Allows for targeted transformation

Phase lamda

Integrates into the bacterial chromosome by recombination between the attP site on the phage and the attB on the chromosomes

Interallelic recombination

Heteroduplex DNA that is create by recombination can have mismatched sequences where the recombining alleles are not identical