Biology Chapter 10- Genetic Recombination (Lecture 5-6)
10.1- Mechanism of Genetic Recombination
• Genetic Recombination requires two DNA molecules that differ from one another in at
least two places, a mechanism for bringing the DNA molecules into close proximity and a
collection of enzymes to ‘cut,’ and ‘paste’ the DNA back together.
• Homologous- Regions of DNA that are similar but not identical
o HOMOLOGY allows DNA on different molecules to line up and recombine
• Enzymatic cutting and pasting of both DNA backbones from each of the two DNA
molecules is required for each recombination event.
o Cutting and pasting four DNA backbones results in one recombination event
Q- WHAT WOULD HAPPEN IF TWO CIRCULAR DNA MOLECULES WERE INVOLVED IN A
SINGLE REOMBINATION EVENT?
A-TWO CIRCULAR MOLECULES ‘FUSE’ TOGETHER AS A RESULT OF A SINGLE
Rare mutations in a DNA sequence of a gene give rise to new alleles. Without this
phenomenon there would be no evolution! 10.2- Genetic Recombination in Bacteria
• Data showed that, for particular bacteria, there are mechanisms to bring DNA from
different cells together to recombine and create genetically different offspring
• Study of bacterial recombination requires detectable genetic differences between strains
• Lederberg and Tatum created strains that were different in their ability to manufacture
certain amino acids and vitamins o Replica plating transfers cells from complete media to minimal media where
auxotrophs fail to grow.
o The picture provides us with experimental evidence for genetic recombination in
o In bacteria, the
DNA of the
• Three primary
DNA into bacterial
cells from the outside:
1. Conjugation-The basis of a kind of sexual reproduction in bacteria
Instead of fusing, bacterial cells conjugate
Contact each other by a long tubular
structure called a sex pilus and then form a
Part or all of the DNA of one cell moves into