Chapter 15 – Genetic Engineering

HOW AND WHY DO SCIENTISTS MANIPULATE DNA IN LIVING CELLS?

SOME REASONS WHY:

• Increase the yield from plants and animals (milk, beef, chicken, corn, soybeans, etc)

• Disease and pest prevention/resistance• Cloning• Medical Research• Gene Therapy• Genetic Testing• Personal identification (DNA fingerprint)

15.1 Selective BreedingSelective Breeding

- Taking advantage of naturally occurring genetic variations to pass wanted traits to the next generation.

Methods used to selectively breed:

1. Hybridization – crossing dissimilar individuals to bring together desirable characteristics from each

Ex. (disease resistance X food producing capacity)

2. Inbreeding – breeding individuals with similar characteristics to ensure unique traits are preserved (pure bred dogs)

15.2 Recombinant DNA (Finding Genes)

Can we change the DNA of a living cell?

1. Cut the DNA using restriction enzymes

2. Build a DNA sequence with the gene or genes desired

3. Enzymes like ligase connect the sticky ends of two DNA pieces together

Recombinant DNA – joining DNAfrom two or more different sources

Plasmids and Genetic Markers

Problem: DNA molecules insertedinto host cells were not replicated:

Solution: Use plasmids to introduce1. Plasmid – a piece of circular

bacterial DNA 2. Plasmids generally contain:

a. a replication start signal (ori),b. restriction enzyme start site (EcoR1)c. genetic markers like antibiotic

resistance genes (tetracycline and ampicillin)

Plasmids and Genetic MarkersRecombination Process using Plasmids

1. The same restriction enzyme is used to cut plasmid and DNA of interest

2. The DNA of interest is joined to the plasmid using ligase

3. Recombined DNA is inserted into the host cell

4. The genetic marker (like antibiotic resistance) identifies the recombined DNA after bacterial growth

Plasmids and Genetic Markers

Use for recombined genes: Human growth hormone (HGH), insulin, gene therapy, resistance of

crops to pests and herbicides, pollution control, designer species

Transgenic Organisms

Transgenic – organisms that contain genes from other species, produced by insertion of recombinant DNA into the genome of a host organism

Used in plants, animals and microorganisms – increased our understanding of gene regulation

Genetically modified plants

Transgenic Organisms

Transgenic Plants – transformed by using bacteria such as Agrobacterium, removing the cell wall or directly injected

Transgenic Animals – transformed by injecting DNA directly into the nucleus of egg cells.

In each case the goal is to have thehost cell combine the recombinantDNA with it’s own chromosomes

CloningClone – A member of a population of genetically identical cells produced from a

single cellSteps in nuclear transplantation cloning:• Nucleus of an unfertilized egg is removed• Egg cell is fused with a donor cell that contains a nucleus• The egg and donor cell are fused using an electric shock• Diploid egg develops into an embryo• Embryo is implanted in the uterine wall of a foster mother.

Animals cloned: frogs, sheep (Dolly 1997), cows, pigs, mice and cats

15.3 Applications of Genetic EngineeringHave you eaten genetically modified (GM) foods this week?

GM Crops – transgenic plants that resist pests, herbicides, disease and result in increased yields.

-Use of these crops is on the rise -Introduced in 1996 (soybean)-As of 2014 GM crops made up 94% of soybeans, 96 % of cotton and 93% of corn

Examples: Roundup ready soybeans, Bt corn, tomatoes, rice, potatoes and stacked varieties (HT and Bt traits) BT Corn Video

15.3 Applications of Genetic Engineering

GM animals – engineered to increaseproduction, nutritional benefit orproduct not typically associated withthat animal.

30% of milk in US is coming fromcows injected with bovine growthhormone (BGH)

In 2008, US approved the sale ofmeat and milk from cloned animals.

15.3 Applications of Genetic EngineeringExamples of GM foods:

Cows – rBGH, increased milk output

Pigs – leaner meat, omega 3 acids

Salmon – GH, shorter time to marketAquabounty - SalmonGoats – spider genes to manufacture silk, antibacterial goat milk

Gene Therapy• Gene Therapy – an absent or faulty gene is replaced

by a normal, working gene.– The first attempted of a gene transfer to cure a

disease occurred in 1990.– Scientist engineer a virus to carry the new gene

into the target cells– Problem: need reliable ways to insert working

genes in target cells and ensure DNA used does no harm.

DNA Fingerprinting

1. Restriction enzymes are used to cut the DNA into fragments containing genes and repeats

2. The restriction fragments are separated according to size using gel electrophoresis

3. The DNA fragments containing repeats are then labeled using radioactive probes. This labeling produces a series of bands – the DNA fingerprint.

DNA Fingerprinting