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