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Learn about the methods of selective breeding and manipulating DNA to create organisms with desired traits. Discover the applications and ethical considerations of genetic engineering.
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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
HybridizationA “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)
Lion x Tiger = Liger Horse x Donkey = Mule
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.
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 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
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??
