Chapter 13GENETIC ENGINEERING

Genetic variation

• How are a great dane and a chihuahua similar?• All dogs are the same species• LOTS of genetic variation!

• How did this happen?• We did it!

Selective breeding

• Selective breeding: a method of breeding organisms with desired characteristics to provide the next generation with that trait

• Takes advantage of natural genetic variation

• Luther Burbank- selectively bred disease-resistant potatoes

hybridization

• Hybridization: breeding technique that crosses dissimilar individuals to bring together the best traits of each

• Hybrid: offspring of hybridization

• Ex: crossing a large sized potato with a potato that is disease-resistant

Or a hybrid car…

…or a mule!

inbreeding

• Inbreeding: continued breeding of individuals with similar (desired) characteristics

• You get the desired traits but…• Increased chance of other defects (ex:

2 recessive alleles)

Genetic variation

• Increased genetic variation = possibility of breeding mutants (but this is a good thing)• Remember the 4 criteria for a gene?

• Mutations are the BIGGEST source of genetic variation

• Whether good or bad, mutations are new to a population and increase diversity

Producing new kinds of organisms

• Treat with radiation or chemicals to mutate

• Bacteria• small and multiply quick/easy to

pass along mutation• Ex: bacteria that digest oil (used in

oil spills)

• Plants• Chemicals prevent chromosome

separation in meiosis• End up with extra sets of

chromosomes (polyploids)

13-2 Manipulating DNA

• What does it mean to “manipulate” DNA?• To change it!

• Selective breeding and inbreeding use natural genetic variation…but its unpredictable!

• Now, we can “rewrite” the code

How do we change dna?

• Must have knowledge of structure and chemical properties

• New technology:• 1. extraction techniques• 2. cut into smaller pieces• 3. identify base sequences• 4. make unlimited copies

1. Dna extraction

• Like in our strawberry lab!

• Open up the cell and nucleus

• Separate DNA from everything else

2. Cutting dna…

• Restriction enzymes: enzyme that cuts DNA at a specific sequence of nucleotides• Very specific

• Recombinant DNA: DNA produced by combining DNA from different sources• Ex: human insulin gene and pig DNA- have

pigs produce insulin

…and separating DNA

• Gel electrophoresis: procedure used to separate + analyze DNA fragments• Place DNA (- charge) at one end of a

gel and apply + charge to the other• Fragments move across gel- smaller

move faster/further• Used to compare/contrast/identify

particular genes

3. Identifying base sequences

• Used to study specific genes, compare, discover functions, etc.

• To “read” the sequence = determine the order of bases

• Sequencing:• Start with unknown strand + DNA

polymerase +nucleotide bases = complimentary strand is made

• Bases are dyed to identify them

• Now, everything is automated

4. Making copies

• Polymerase chain reaction (PCR): technology that allows scientists to make many copies of a gene

• How it works:• Heat DNA- strands separate• Cool and add primers- short pieces of DNA that

tell DNA polymerase to start working• Add free nucleotide bases + DNA polymerase• Makes a new stand- like artificial DNA

replication!

13-3 cell transformation

• What is transformation?

• Taking in DNA from outside the cell- this “external” DNA then becomes part of the new cell’s DNA• DNA MUST be integrated into

a chromosome!

• Recombinant DNA!

Transforming bacteria

• Plasmid: small circular DNA molecule

• Why plasmids?• Replicate easily so foreign

DNA will then be replicated• Genetic marker: a gene that

distinguishes bacteria with foreign DNA plasmid from ”regular” bacteria• Antibiotics resistant genes

used alot

Transforming plant cells

• Use bacterium that inserts a plasmid with manipulated foreign DNA into plant cells

• Can also:• Take up DNA when cell wall is removed• Inject DNA directly into plant cells

• Either way, DNA MUST be integrated into the chromosome

Transforming animal cells

• Cells are large enough for direct injection of DNA

• Enzymes used to cut and insert DNA into chromosome

• May also use genetic markers

• Gene replacement- replace one gene with another

13-4 Applications of ge

• GE = biotechnology

• Can we combine plant and animal genes?• YES!

• Luciferase enzyme (firefly glow) + tobacco plant = a glowing plant

Transgenic organisms

• Transgenic organism: an organism that contains genes from a different organism

• Gene from one inserted into the cell of another

• These transformed cells = a new organism!

Transgenic microorganisms

• Insert human gene for proteins into bacteria

• Bacteria used to “harvest” human proteins• Ex: insulin, growth factors, clotting

factors

Transgenic plants

• Examples:• Plants with natural insecticides• Plants that will resist weed-killing

chemicals• Rice with added vitamin A

Transgenic animals

• For research:• mice with human immune systems

• For food:• Livestock with added growth hormone-

grow faster/leaner• Chicken that is resistant to food

poisoning bacteria• Milk that produces human proteins in

it

cloning

• Clone: a member of a population of genetically identical cells produced from a single cell

• Single-celled bacteria= easy to clone

• Multicellular organism= more difficult

• “Dolly” the sheep- cloned by Ian Wilmut in 1997

How did he do it?

• De-nucleate an egg cell

• Donor nucleus fuses to the de-nucleated cell• Fused using an electric shock

• Cell will begin to divide- form an embryo

• Embryo is placed in foster mom’s uterus

• Development and birth happen as normally does

cloning

Cloning Pros and cons

• Pros• Ability to reproduce transgenic animals• Ability to reproduce endangered species

• Cons• Genetic defects• Unknown side effects

• What else?