Chapter 13 – Genetic Engineering

L2 Biology

Has Bonnie been bred by selective breeding?

Selective Breeding• Choose organisms with the desired traits

and breed them, so the next generation also has those traits

• Nearly all domesticated animals and crops

• Luther Burbank (1849-1926) developed >800 diff varieties of plants in his lifetime

Hybridization

• Breed two dissimilar organisms

• In plants – often results in better lines – hybrids are larger, stronger, etc

• In animals – hybrids produced may be weaker and sterile

– Ex – wolf x dog ---- weak wolf-dog

– Ex – horse x donkey ---- mule (sterile)

Horse x Donkey = Mule

Lion x Tiger = Liger

Inbreeding

• Breeding two organisms that are

very similar to produce offspring

with the desired traits. – Ex – dog breeds

•Risks – might bring together two individuals that carry bad recessive genes – many purebred dogs have genetic disorders that mutts don’t get.

Increasing Variation• Induce mutations – the ultimate source of

genetic variations among a group of organisms– Mutagens used – radiation and chemicals– Some organisms are formed that have more

desirable variations.

Producing new kinds of bacteria

• Can expose millions of bacteria at one time to radiation – increases chances of producing a successful mutant. – Ex – bacteria that can digest oil have been

produced this way

                                                                                                                 

                

Producing new kinds of plants:

• Drugs that prevent chromosomal separation in meiosis have been used to create plants that have more than two sets of chromosomes (2n). These are called polyploid plants. – Ex – bananas, citrus fruit, strawberries, many

ornamental flowers

                                             

Diploid corn

Tetraploid corn

Manipulating DNA – tools of the molecular biologist

• DNA extraction – open the cells and separate DNA from all the other cell parts. – Remember the kiwi lab?

• Cutting DNA

• Use restriction enzymes

– each one cuts DNA at a

specific sequence of nucleotides.

• This will make different

lengths of DNA

• Separating DNA – Gel Electrophoresis– Place fragments at one end of a porous gel – we

use agarose gel– Apply an electric current – The DNA is

negatively charged and will travel toward the positive end of the gel.

– The larger pieces of DNA move slower, the smaller ones faster.

– Used to compare genomes of different organisms or different individuals.

– Also used to locate and identify one particular gene out of an individual’s genome.

Click here for animation about gel electrophoresis

Using the DNA Sequence

• Sequence can be read, studied, and changed.

• Techniques used to study DNA sequences: – Use DNA polymerase and the 4 DNA bases to

produce a new DNA strand complementary to unknown strand – some of the bases are dyed.

• Dye-labeled strands are then separated using gel electrophoresis and the order of the bands tells the DNA sequence of the unknown strand.

• Cutting and Pasting – make recombinant DNA (DNA from two different organisms).

– Cut out the gene to be inserted, use same restriction enzyme to cut the receiving DNA strand, attach the two DNA strands

Making Copies

• Polymerase Chain Reaction (PCR) is used to make many copies of the same piece of DNA like a photocopy machine makes copies of papers.

• This is useful if there is only a very small sample of DNA available (as that found in a small blood drop at a crime scene)

Cell Transformation

• A cell takes in DNA from outside the cell and that DNA then becomes part of the cell’s DNA.

• Bacteria – place DNA in the solution that bacteria live in, and some of that DNA will be taken in by the bacteria cells.

Bacteria Transformation using Recombinant DNA

• Cut a gene with a restriction enzyme out of a human cell (ex – gene for insulin or growth hormone work well)

• Cut a bacterial plasmid using the same restriction enzyme (DNA ends will be complementary)

• Insert Human gene into bacterial plasmid• Insert plasmid back into bacterial cell• Bacteria will multiply, and all offspring will have

that gene – these bacteria will then follow the directions of the human gene and make the protein coded for (insulin or human growth hormone)

Transforming Plant Cells

• Use bacterial plasmid to insert desired gene into DNA of a plant

Transforming Animal Cells– Directly inject DNA into the nucleus of an egg

– it will become part of the chromosomes.

• Has been used to replace specific genes.

Glowing mouse cells in embryos that were made from sperm given the gene for bioluminescence from jellyfish – now all the cells glow!

Applications of Genetic Engineering

• Gene for luciferase was isolated from fireflies and inserted into tobacco plants – they glowed!

• Transgenic organisms – contain genes from other species

A transgenic mouse, which carriesa jellyfish gene, glows green underfluorescent light.  

Transgenic Organisms

• Bacteria - Make human proteins like insulin

• Plants – 52% of soybeans, 25% of corn in US in year 2000. Some produce natural insecticide, some resist weed-killers, may soon be used to produce human antibodies; rice with vitamin A.

•Animals – mice with immune systems like humans; farm animals that grow faster and larger with extra copies of growth hormone genes; animals with leaner meat; chickens resistant to bacterial infections.

Cloning • Clone – member of a population

of genetically identical cells

produced from a single cell.

• 1996 – Dolly cloned –

1st mammal (sheep) cloned.

• She got arthritis several years

earlier than most sheep

• Died in 2003