Genetic Engineering

Georgia Performance Standards:

• Examine the use of DNA technology in

forensics, medicine, and agriculture

Essential Questions:

• Should there be limits on how DNA technology is used?• How is DNA technology applied to solving problems?

Student Outcomes:

• How DNA comparison is used in forensic science

• The process of genetic engineering through the use of recombinant DNA

• Examine and question complex bioethical issues involving the use of DNA technology in modern medicine, industry, agriculture and forensics

Warm-up:

• A New Breed

• The tomatoes in your salad and the dog in your backyard are a result of selective breeding.

• Over thousands of years, humans have developed breeds of animals and plants that have desirable characteristics.

• How do breeders predict the results of crossing individuals with different traits?

Warm-up:1. Think of two very different breeds of dogs that are

familiar to you. On a sheet of paper, construct a table that has the following three heads: the name of each of the two dog breeds, and “Cross-Breed.”

2. The rows of the table should be labeled with characteristics found in both breeds of dogs. Examples might include size, color, type of coat, intelligence, aggression, and so on.

3. Fill in the column for each of the two dog breeds. In the column labeled “Cross-Breed,” write in the characteristic you would expect to see in a cross between the two breeds you have selected.

Selective Breeding

• Selective Breeding- a method of improving a species by allowing only those individual organisms with desired characteristics to produce the next generation– Hybridization– Inbreeding

Hybridization:

• Hybridization is a breeding technique that involves crossing different individuals to bring together the best traits of both organisms

– Ex: combining the disease resistance of one plant with the food-producing capacity of another produces a hardier plant that increased food supply.

Inbreeding 

• Inbreeding is the continued breeding of individuals with similar characteristics.

• Used to maintain desired characteristics

• Inbreeding helps to ensure that the characteristics that make each breed unique will be preserved.

• Risks: Most of the members of a breed are genetically similar and genetic defects can arise.

which crosses

consists of

Selective Breeding

for example for

example

Organism breed A

Organism breed A

Organism breed B

Retains desired characteristics

Combines desired characteristics

which

which crosses

which

Concept Map

Inbreeding Hybridization

Similar Organisms

DissimilarOrganisms

Increasing Variation

• Sometimes breeders want more variation than exists in nature.    

• Breeders can increase the genetic variation in a population by inducing mutations, which are the ultimate source of genetic variability. – Radiation– Chemicals

Plant Breeding

•  Drugs used in plant breeding sometimes cause plants to produce cells that have double or triple the normal number of chromosomes.

• Plants grown from such cells are called polyploid because they have many sets of chromosomes.

• Polyploidy produces larger and stronger plants, which increase the food supply for humans.

Checkpoint Questions:1. Give one example of selective breeding.

2. Relate genetic variation and mutations to each other.

3. How might a breeder induce mutations?

4. What is polyploidy?

5. Suggest ways that plants could be altered to improve the world’s food supply.

Manipulating DNA:

• How are changes made to DNA?  

• Scientists use their knowledge of the structure of DNA and its chemical properties to study and change DNA molecules.

• Different techniques are used:– to extract DNA from cells– to cut DNA into smaller pieces– to identify the sequence of bases in a DNA molecule– to make unlimited copies of DNA.

Genetic engineering• Genetic Engineering - making changes in

the DNA code of a living organism.– Process:

• DNA extraction• Cutting DNA• Separating DNA• Reading the sequence• Cutting and pasting• Making copies

Molecular Biology

DNA Extraction

• How do biologists get DNA out of a cell?

• DNA can be extracted from most cells by a simple chemical procedure:

– The cells are opened and the DNA is separated from the other cell parts.

Cutting DNA

•  DNA molecules from most organisms are much too large to be analyzed, so biologists cut them precisely into smaller fragments using restriction enzymes.

• Restriction enzymes cut DNA at a specific sequence of nucleotides. – Very precise

Restriction Enzymes

•This drawing shows how restriction enzymes are used to edit DNA.

•The restriction enzyme EcoRI, for example, finds the sequence CTTAAG on DNA.

•Then, the enzyme cuts the molecule at each occurrence of CTTAAG.

•Different restriction enzymes recognize and cut different sequences of nucleotides on DNA molecules. VIDEO

Separating DNA • In gel electrophoresis, a

mixture of DNA fragments is placed at one end of a porous gel, and an electric voltage is applied to the gel.

• When the power is turned on, DNA molecules, which are negatively charged, move toward the positive end of the gel.

• The smaller the DNA fragment, the faster it moves.

• Uses:– Comparing

genomes of different organisms or individuals.

– Locating and identifying one particular gene out of the millions of genes in an individual’s genome.

DNA plus restriction enzyme

Mixture of DNA fragments

Gel

Power source

Longer fragments

Shorter fragments

Gel Electrophoresis

Using the Sequence of DNA:

• “Reading” a DNA sequence is now an automated process.

• The pattern of colored bands (Fluorescently labeled nucleotides) tells the exact sequence of bases in the DNA.

• Each color corresponds to a specific nucleotide base (A, G, C, and T)

Fluorescent dye

Single strand of DNA

Strand broken after A

Strand broken after C

Strand broken after G

Strand broken after T

Power source

Gel

DNA Sequencing

Cutting and Pasting 

• Enzymes make it possible to take a gene from one organism and attach it to the DNA of another organism.

• Such DNA molecules are sometimes called recombinant DNA because they are produced by combining DNA from different sources.

Making Copies

• In order to study genes, biologists often need to make many copies of a particular gene.

• A technique known as polymerase chain reaction (PCR) allows biologists to make copies of DNA.

– PCR Process:

1. DNA is heated to separate strands

2. DNA is cooled to allow primers to bind

3. DNA polymerase copies the strands

PCR:Polymerase ChainReaction

VIDEO

Checkpoint Questions:

1. Describe the process scientists use to manipulate DNA.

2. Why might a scientist want to know the sequence of a DNA molecule?

3. How does gel electrophoresis work?

4. Which technique can be used to make multiple copies of a gene? What are the basic steps in this procedure?

5. How is genetic engineering like computer programming?

Cell Transformation– During Cell Transformation, a cell takes in

DNA from outside the cell. • Plant and animal

– This external DNA becomes a part of the cell’s DNA. • One way to make recombinant DNA is to

insert a human gene into bacterial DNA. • The new combination of genes is then

returned to a bacterial cell, and the bacteria can produce the human protein.

• video

Transforming Bacteria

• Recombinant DNA is used.

• The foreign DNA is first joined to a small, circular DNA molecule known as a plasmid. – Plasmids have a DNA sequence that serves

as a bacterial origin of replication. – Plasmids have a genetic marker—a gene

that makes it possible to distinguish bacteria that carry the plasmid from those that don’t.

Transforming Bacteria

Plant Cell Transformation

• Recombinant plasmids can be used to infect plant cells.

• DNA can also be injected directly into some plant cells.

• Cells transformed by either procedure can be cultured to produce adult plants.    

•

Recombinant plasmid

Gene to be transferred

Agrobacterium tumefaciens

Cellular DNA

Transformed bacteria introduce plasmids into plant cells

Plant cell colonies

Complete plant is generated from transformed cell

Inside plant cell, Agrobacterium inserts part of its DNA into host cell chromosome

Plant Cell Transformation

Animal Cell Transformation:Knockout Genes

• Recombinant DNA can replace a gene in an animal’s genome.

• The ends of the recombinant DNA recombine with sequences in the host cell DNA.

• When the recombinant DNA is inserted into the target location, the host cell’s original gene is lost or knocked out of its place.

Knockout Genes

Checkpoint Questions:

1. What is transformation?

2. How can you tell if a transformation experiment has been successful?

3. How are genetic markers related to transformation?

4. What are two features that make plasmids useful for transforming cells?

5. Compare the transformation of a prokaryotic cell with the transformation of a eukaryotic cell.

Applications of Genetic Engineering

• Scientists have developed many transgenic organisms, which are organisms that contain genes from other organisms. – scientists have removed a gene for green

fluorescent protein from a jellyfish and tried to insert it into a monkey.

Applications of Genetic Engineering

• Transgenic animals are often used in research.

– What might be the benefit to medical research of a mouse whose immune system is genetically altered to mimic some aspect of the human immune system?

• Transgenic plants and animals may have increased value as food sources.

– What might happen to native species if transgenic animals or plants were released into the wild?

Transgenic Organisms:

• The universal nature of genetic mechanisms makes it possible to construct organisms that are transgenic, meaning that they contain genes from other organisms.

• A gene from one organism can be inserted into cells from another organism.

• These transformed cells can then be used to grow new organisms.

Transgenic Bacteria or Yeast:

• Transgenic bacteria reproduce rapidly and are easy to grow.

• Therefore they now produce a host of important substances useful for health and industry. – human insulin, growth hormone, and

clotting factor

Transgenic Animals:• Transgenic animals have been used to study genes and to

improve the food supply – Strains of mice

• produced with human genes that make their immune systems act similarly to those of humans.

• study the effects of diseases on the human immune system.

– Transgenic livestock • produced with extra copies of growth hormone genes.• such animals grow faster and produce meat that is less

fatty than that from ordinary animals.

– Transgenic chickens • resistant to the bacterial infections that sometimes

cause food poisoning.

Transgenic Plants:

• Transgenic plants help to increase our food supply.

• Genes produce a natural insecticide (this avoids synthetic pesticide use).

• Genes that enable them to resist weed-killing chemicals (allows farmers to grow more food by controlling weeds.

• Human antibodies that can be used to fight disease;

• Plastics that can now be produced only from petroleum

• Foods that are resistant to rot and spoilage.

Cloning:

• A clone is a member of a population of genetically identical cells produced from a single cell.

• Cloned colonies of bacteria and other microorganisms are easy to grow, but this is not always true of multicellular organisms, especially animals.

Cloning:

• Clones are used for medical and scientific value, but also causes ethical issues.

• In 1997, Scottish scientist Ian Wilmut stunned biologists by announcing that he had cloned a sheep

Cloning

A body cell is taken from a donor animal.

An egg cell is taken from a donor animal.

The fused cell begins dividing, becoming an embryo.

The nucleus is removed from the egg.

The body cell and egg are fused by electric shock.

The embryo is implanted into the uterus of a foster mother.

The embryo develops into a cloned animal.

A donor cell is taken from a sheep’s udder. Donor

Nucleus

These two cells are fused using an electric shock.

Fused Cell

The fused cell begins dividing normally.

EmbryoThe embryo is placed in the uterus of a foster mother.Foster

Mother

The embryo develops normally into a lamb—Dolly

Cloned Lamb

Egg Cell

An egg cell is taken from an adult female sheep.

The nucleus of the egg cell is removed.

Section 13-4

Cloning of the First Mammal

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Checkpoint Questions:1. List one practical application for each of the

following: transgenic bacteria, transgenic animals, transgenic plants.

2. What is a transgenic organism?

3. What basic steps were followed to produce Dolly?

4. List reasons you would or would not be concerned about eating genetically modified food.

Warm-up:

• As you become more aware of scientific advances in genetics, you might realize that with the ability to manipulate genes, there comes responsibility.

• This ability provides an opportunity to improve the lives of many people.

• But there is also a potential for errors or intentional misuse of the technology.

Warm-up:Working with a partner, answer the following questions.

1. In what type of situation do you think genetic engineering—changing the genes of organisms—is warranted? Explain your reasoning about your position. If you do not think that genetic engineering is ever warranted, explain your reasons for your position.

2. In what type of situation do you think genetic engineering might be misused? Suggest limits that might be placed on the manipulation of genes to avoid its misuse.

DNA fingerprinting

• Analysis of sections of DNA that have little or no known function, but vary widely from one individual to another, in order to identify individuals

• The reliability of DNA evidence has helped convict criminals as well as overturn many convictions.

Restriction enzyme

Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA varies from person to person. Here, one sample has 12 repeats between genes A and B, while the second sample has 9 repeats.

Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Note that the repeat fragments from these two samples are of different lengths.

The DNA fragments are separated according to size using gel electrophoresis. The fragments containing repeats are then labeled using radioactive probes. This produces a series of bands—the DNA fingerprint.

Section 14-3Figure 14-18 DNA Fingerprinting

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The Human Genome Project:

• The Human Genome Project is an attempt to sequence all human DNA.

• VIDEO

Gene Therapy• Curing genetic disorders by gene therapy.

• Gene therapy is the process of changing the gene that causes a genetic disorder.    

• In gene therapy, an absent or faulty gene is replaced by a normal, working gene.

• This way, the body can make the correct protein or enzyme it needs, which eliminates the cause of the disorder.

Normal hemoglobin gene

Bone marrow cell

Chromosomes

Genetically engineered virus

Nucleus

Bone marrow

Section 14-3Figure 14-21 Gene Therapy

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Think About It…

• What will happen to the human species if we gain the opportunity to design our bodies…

Checkpoint Questions:

1. What is the Human Genome Project?

2.  Describe how gene therapy works.

3. Name two common uses for DNA testing.

4. Describe how molecular biologists identify genes in sequences of DNA.

5. Do you think it should be legal for people to use genetic engineering to affect their children’s characteristics? Give reasons for your answer.