BMB 251 - Exam 2 - Homologous Recombination (5.3)

the homologous recombination machinery is used by cells to

repair double-stranded breaks in DNA
exchange genetic content between the maternal and paternal alleles of genes on homologous chromosomes during the production of the germ cells (egg and sperm) (fig 5-53)

hallmarks of homologous recombination (the following three)

where do DNA hybridization and heteroduplex form

between the homologs at identical or very similar DNA sequences (fig 5-47)

homologous recombination requires what

extensive regions of homology between the two DNA helices (fig 5-54)

the enzymes that catalyze homologous recombination include:

RecA (of e.coli)
Rad 51 (of eukaryotes) - both ATPase and DNA binding proteins (fig 5-49)
in addition to many other accessory proteins

outcomes of homologous recombination

reciprocal exchange, non-reciprocal exchange or gene conversion

reciprocal exchange

an equal exchange of genetic information between two DNA fragments (ex. crossing over during meiosis)

reciprocal exchange is the reason for what

underlying the 2:2 Mendelian segregation of alleles in genetic crosses (slide)

non-reciprocal exchange or gene conversion

there is a seemingly unequal exchange of information between the two chromosomes

what is the reason for a non-reciprocal exchange or gene conversion outcome

that the regions of one of the DNA fragments becomes a "copy" of the other DNA fragment

some of the processes of DNA repair are involved in gene conversion (true/false)

true

gene conversion is the reason for what

underlying the occasional non-Mendelian segregation of alleles during meiosis (ex. 3:1 instead of 2:2) (fig 5-59)

other types of recombination

transposition, illegitimate recombination

transposition

class of non-homologous recombination performed by transposons in which small defined fragments of the chromosome "hop" from one location to another

transposons

"jumping genes"

there is very little if any requirement for homology or similarity between the donor and target DNA molecules (true/false)

true

examples of transposition

the class of DNA-only transposons (fig 5-60, 61)

DNA-only transposons (fig 5-60, 61)

contribute to the spread of antibiotic resistance in bacteria

illegitimate recombination

NO apparent homology between the interacting DNA sequences

illegitimate recombination happens (before, after) the transformation of DNA into genomes of higher eukaryotic organisms

after