Microbiology Microbial Genetics IV

Genetic Recombination

exchange of similar (homologous) nucleotide sequences between two DNA molecules

ex. Crossing over during meiosis to form gametes (sperm and egg)

23 pairs of chromosomes; one from mom, one from dad, form a pair that is homologous

green(mom), red(dad) cross over, resulting in a little bit of red being present in the green(moms chromosome) and vice versa

Vertical Gene Transfer

passing of genes down from parent to offspring

grandfather → mother → children, etc

Horizontal Gene Transfer

genes passed laterally in same generation; recombination of transferred genes

prokaryotes ONLY; donor & recipient (recombinant) cells

the donor can only give a FRAGMENT of its DNA horizontally to a recipient, i.e replacing a little bit of a red circle(recipients DNA) with a fragment of black(donors DNA)

Transformation

recipient takes up DNA fragments in environment from a dead cell

antibiotic resistance has spread this way

Conjugation

“bacterial sex”

Fertility plasmid (F Plasmid); allows bacteria to form special pilus, allowing plasmid to transfer to recipient

antibiotic resistance has spread this way

donor cell attaches to a recipient cell with its pilus, potentially drawing cells together; one strand of F plasmid DNA transfers to the recipient, where it is then synthesized

donor cell keeps a strand of plasmid to resynthesize it once more for donation/personal use.

Transduction

new assembling phage accidentally package piece of bacterial chromosome; transferred to a new cell when the phage infects it

dead end for phage but could be good for bacteria; ex. antibiotic resistance