chapter 13 genetic engineering. selective breeding choose organisms with the desired traits and...

Chapter 13 Genetic Engineering

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

Hybridization

A “Hybrid”

• 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.

• 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.

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.

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 under

fluorescent 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

ETHICS…• Reproductive cloning would present the

potential of creating a human OR animal that is genetically identical to another person who has previously existed (maybe extinct) or who still exists

good or bad?

Ethics

• May conflict with long-standing religious and societal values about human dignity, possibly infringing upon principles of individual freedom, identity and autonomy

Ethics

• Therapeutic cloning would require the destruction of human embryos in the test tube.

Ethics• Opponents argue that

using this technique to collect embryonic stem cells is wrong, regardless of whether such cells are used to benefit sick or injured people.

The Goods!!

• Therapeutic cloning WOULD offer the potential for treating humans suffering from disease or injury

• Could help sterile couples

fulfill their dream of

parenthood

The Goods!!

• Human cloning is also a GREAT way to avoid passing on a bad gene that runs in the family without having to undergo embryo screening or embryo selection

• “knock out” the bad genes… good or bad??

Ethics… Its your call…