Ch 13 Genetic Engineering 1 Selective Breeding Choose

Ch 13 – Genetic Engineering 1

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

Hy b rid iza tio n • 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.

+ Arctic fish DNA = A strawberry resistant to frost strawberry GMO’s (Genetically modified organisms)

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 (2 n). 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 pea lab?

DNA Extraction • Chemical treatments cause cells and nuclei to burst • The DNA is inherently sticky, sticky and can be pulled out of the mixture • This is called “spooling” DNA 11

“Spooled” DNA 12

Cutting DNA • Restriction enzymes cut DNA at specific sequences • Useful to divide DNA into manageable fragments 13

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Electrophoresis • DNA can be separated based on size and charge • The phosphate groups are negatively charged • DNA is placed in a gel and electricity is run through 15

Electrophoresis • Negative DNA moves toward the positive end • Smaller fragments move farther and faster 16

Electrophoresis 17

Click here for animation about gel electrophoresis

Steps in DNA Sequencing • Many copies of a single strand of DNA are placed in a test tube • DNA polymerase is added • A mixture of nucleotides is added some of which have dye molecules attached • Each base (A, T, C, G) has a different color dye 19

Steps in DNA Sequencing • By chance, some dyed nucleotides & some regular ones are added • Dye molecules are large and stop the chain from growing 20

DNA Sequencing • The result is DNA fragments of multiple sizes with colors that can be identified 21

DNA Sequencing • After the gel separates the resulting fragments by size, we 'read' the sequence from bottom to top. 22

Copying DNA • Polymerase Chain Reaction • Also called PCR • A method of making many copies of a piece of DNA 23

Steps in Copying DNA • A DNA molecule is placed in a small test tube • DNA polymerase that can work at high temps is added 24

Steps in Copying DNA • The DNA is heated to separate the two strands • Primers, Primers short pieces of DNA complementary to the ends of the molecule to be copied, are added 25

Copying DNA • The tube is cooled, and DNA polymerase adds new bases to the separated strands 26

PCR Large amounts of DNA can be made from a small starting sample 27

Cloning • Clone a member of a group of genetically identical cells • May be produced by asexual reproduction (mitosis) 28

Cloning organisms • A body cell from one organism and an egg cell from another are fused • The resulting cell divides like a normal embryo 29

Cloning “Dolly” 30

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)

Bacterial plasmids in gene cloning 33

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 carries a jellyfish gene, glows green under fluorescent light.

• http: //learn. genetics. utah. edu/content/begin/dna/firefly/ Tobacco Plant containing Luciferin gene from Firefly 35

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.