Chapter 15: Genetic EngineeringSection 15-2: Recombinant DNA
Copying DNA Breeders relied on natural variation
produced by unpredictable mutations Genetic engineers today can transfer
genes from one organism to another, creating new living things
Need to isolate DNA, cut it with REs, separate it with gel electrophoresis
Finding Genes If a scientists is looking for a particular
gene, they can use a technique called Southern blotting analysis
Example: In 1987 Douglas Prasher was looking for
the gene in jellyfish that creates GFP, green fluorescent protein
Wanted to isolate and use this gene as a marker
Finding Genes Figured out the most likely mRNA
sequence for part of the amino acid sequence
Compared to thousands of others until he found the exact sequence in the jellyfish
Found the actual gene by taking a gel with jellyfish DNA that had been cut with REs
Found fragment that bound exactly to mRNA – this was the gene
Polymerase Chain Reaction Technique used to make multiple copies
of a gene once it is found DNA heated to separate strands Cooled, primers added DNA polymerase produces
complementary strands Repeated over and over
Changing DNA Scientists can create custom DNA
molecules and insert them into living cells
Machines called DNA synthesizers produce short segments of DNA which can then be joined to natural sequences using DNA ligase or other enzyme for splicing
Combining DNA Fragments If two DNA sequences from two different
organisms are cut with the same RE, their sticky ends can be matched and they can be permanently bonded
Resulting molecules called recombinant DNA (recombinant DNA technology)
Plasmids and Genetic Markers Sometimes genes were “lost” once they
were inserted because they did not replicate along with the cell’s regular DNA
Now add the genes plus a replication “start” signal
Technique often used to create recombinant plasmids in bacteria (extra, circular DNA), yeasts
Use markers to identify inserted genes
Transgenic Organisms Organisms that contain genes from
other species Produced by inserting recombinant DNA
into genome of host organism Contain genetic markers
Transgenic Plants Plant cells often transformed with Argobacterium, which in nature inserts a gene into plants that produces tumors
Scientists deactivate the tumor gene, replace it with recombinant DNA, which then transforms plant cells
Transgenic Plants Can also be produced by removing cell
wall and allowing plant cell to pick up extra DNA, or inject DNA directly
Transgenic Animals If the egg cell is large enough, DNA can
be injected directly into nucleus and hopefully inserted into chromosomes
Now we can also eliminate genes by inserting new recombinant DNA within them
Cloning A clone is a member of a genetically
identical cells produced from a single cell
Uses a single cell from an adult organism to grow an entirely new organism – genetically identical
Animal cloning involves nuclear transplantation
Animal Cloning Nucleus of unfertilized egg removed Egg cell fused with donor nucleus taken
from adult Resulting diploid cell develops into
embryo Embryo implanted into uterine wall of
foster mother Develops until birth
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