Homologous Recombination Flashcards
Homologous recombination
Exchange between chromosomes that have the same #, but aren’t identical (have regions of sameness)
Site-directed recombination
Recombination between specific sequences
Floxing
Example of site-directed recombination
Gene of interest is flanked by loxP sites
Cre recombinase catalyzes recombination of loxP sites
3 processes during which homologous recombination occurs
- Meiotic recombination (crossing over: shuffling of linked alleles)
- Double strand break repair (replication: damaged piece is repaired by recombination with complementary chromosome)
- Mating type switching in yeast
Crossing over
Homologous chromatids exchange portions of themselves
Occurs every time meiosis happens
Synaptonemal complex
Zipperlike complex of proteins that forms between 2 homologous chromosomes during meiosis
Recombination hot spot
Likely spot of recombination
Euchromatin
Genes are closer together on real map than on a genetic map (large gap: more room for recombination)
Recombination cold spot
Unlikely spot of recombination
Near centromere (tightly packed)
Heterochromatin
How much similarity is necessary to be counted as homologous?
~100 bp similarity
Major steps in homologous recombination
- Double strand break introduced, leading to alignment of chromosomes
or
Alignment of chromosomes - Double strand breaks introduced by endonucleases and processed into ssDNA
- Strand invasion (ssDNA base pairs with homologous chromosome)
- Holliday junction formation and branch migration (Holliday junction moves down DNA, increasing amount of DNA exchanged)
- Resolution (Holliday junction is rotated and cleaved to form 2 separate dsDNA molecules)
Heteroduplex regions
Regions of chromosomes that aren’t completely complementary
Recombination between homologous chromosomes
What DNA is covered with during homologous recombination
Proteins: protect DNA from degradation
Splice/recombination product
Product of homologous recombination that has different alleles from the parent
Patch/non-recombination product
Product of homologous recombination that has the same combination of alleles as the parent except for 1 allele
3 genetic consequences of recombination
- Variation
- Proper disjunction
- Gene conversion
Gene conversion
Following recombination, sister chromatids are no longer identical: mismatch repair proteins change 1 allele so that it matches the other chromatid’s (which allele is swapped is random: could be same as sister chromatid or same as chromatid with whom recombination occurred)
