12.4 How Is Biotechnology Used In Agriculture?

12.4 How Is Biotechnology Used In Agriculture?

Fig. 12-9(2)

recombinantplasmid withBt gene

Bt genes and plasmids, both with the samecomplementary sticky ends, are mixed together;DNA ligase bonds the Bt genes into the plasmids.


11. Plasmid-transformed bacteria insert the Bt gene into a plant.

12. Certain bacteria can enter the cells of specific types of plants.

13. These bacteria are transformed with the recombinant plasmids.


Fig. 12-9(3)

bacteriumbacterialchromosome recombinant

plasmids Bacteria are transformed with the recombinant plasmids.


14. When the transformed bacteria enter a plant cell, the plasmids insert their DNA, including the Bt gene, into the plant’s chromosomes.


Fig. 12-9(4)

Bt gene

plant cellplant chromosome

Transgenic bacteria enter the plant cells, and Bt genesare inserted into the chromosomes of the plant cells.


15. Therefore, any time that a plant cell divides, all of its daughter cells inherit the Bt gene.

16. Hormones stimulate the transgenic plant cells to divide and differentiate into entire plants.

17. These plants are bred to one another, or to other plants, to create commercially valuable plants that resist insect attack.


• Bt plants resist insect attack.

Fig. 12-10


• Genetically modified plants may produce medicines.– Similar techniques can be used to insert medically

useful genes into plants, producing medicines.– Plants could be made to produce human antibodies

that would combat various diseases.


• Genetically modified plants may produce medicines (continued).– A direct injection of plant-produced antibodies soon

after infection might cure the resulting disease much more rapidly than waiting for the immune system to handle the pathogens.

– Plant-derived antibodies against bacteria that cause tooth decay and non-Hodgkins lymphoma could be produced cheaply, enhancing the availability of therapies.


• Genetically modified animals may be useful in agriculture and medicine.– Making transgenic animals involves injecting the

desired DNA into a fertilized egg, which is then implanted into a surrogate mother.

– If the offspring are healthy and express the foreign gene, they are then bred together to produce homozygous transgenic organisms.

– Companies have developed salmon and trout with modified or added growth-hormone genes, which make the fish grow much faster than wild fish.


• Genetically modified animals may be useful in agriculture and medicine (continued).– Because medicines are generally more valuable than

meat, many researchers are developing animals that will produce medicines.

• Alpha-1-antitrypsin: a protein that may prove value in treating cystic fibrosis

• Erythropoietin: a hormone that stimulates red blood cell production

• Clotting factors for treating hemophilia

12.5 How Is Biotechnology Used To Learn About The Human Genome?

• In 1990, the Human Genome Project was launched to determine the nucleotide sequence of all DNA in our entire set of genes, called the human genome.– The human genome contains only about 21,000

genes comprising only 2% of the DNA.– It is not known what the 98% of the remaining DNA

does.

12.5 How Is Biotechnology Used To Learn About The Human Genome?

• Knowing the human genome will help:– Find out what many unknown proteins do.– Understand human disease.– Diagnose genetic disorders and devise treatments or

cures.– Comparing the human genome to that of other

organisms will help us understand our place in the evolution of life.

12.6 How Is Biotechnology Used For Medical Diagnosis And Treatment?

• DNA technology can be used to diagnose inherited disorders.– People inherit a genetic disease because they inherit

one or more dysfunctional alleles.– Defective alleles have different nucleotide

sequences than functional alleles.– Two methods are currently used to find out if a

person carries a normal allele or a malfunctioning allele.


• Restriction enzymes may cut different alleles at different locations. – A defective allele may be cut by a particular

restriction enzyme, while a functional allele will not.


• Diagnosing sickle-cell anemia with restriction enzymes

Fig. 12-11a

large pieceof DNA

small pieceof DNA

MstIIcut #1

MstIIcut #3

MstIIcut #2

DNA probe

(a) MstII cuts the normal globin allele into two piecesthat can be labeled by a probe


• Diagnosing sickle-cell anemia with restriction enzymes (continued)

Fig. 12-11b

very large pieceof DNA

MstIIcut #1

MstIIcut #3

DNA probe

(b)MstII cuts the sickle-cell allele into one very largepiece that can be labeled by the same probe

larger piecesof DNA

smaller piecesof DNA

Homozygoussickle-cell: oneband of verylarge DNApieces

Heterozygous:three bands

(c) Analysis of globin alleles by gel electrophoresis

Homozygous normal:one band of large DNApieces and one bandof small DNA pieces


• Diagnosing sickle-cell anemia with restriction enzymes (continued)

Fig. 12-11c


• Different alleles bind to different DNA probes.– This method has been applied to characterizing the

1,000 different CFTR (cystic fibrosis) protein alleles.


• A cystic fibrosis diagnostic array

Fig. 12-12a,b

DNA probefor normalCFTR allele

DNA probes for10 different mutantCFTR alleles

(a) Linear array of probes for cystic fibrosis

colored molecule

piece of patient’sDNA

(b) CFTR allele labeled with a coloredmolecule

A T A TC C T T T GG T G


Fig. 12-12c

Homozygous for normal CFTR alleles—the person is phenotypically normal

One normal and one defective CFTR allele—the person is phenotypically normal

Two different defective CFTR alleles—the person develops cystic fibrosis

#1

(c) Linear arrays with labeled DNA samplesfrom three different people

#2

#3


• Someday, physicians may be able to use an array containing hundreds or thousands of DNA probes for hundreds of disease-related alleles.

• This will help them determine the susceptibility for the diseases that each patient has, and to tailor the patient’s medical care accordingly.


• Arrays containing probes for thousands of human genes are already manufactured.

• These arrays can be tailored to investigate gene activity in specific diseases, such as breast cancer.


• A human DNA microarray

Fig. 12-13


• DNA technology can be used to treat disease.– Thanks to recombinant DNA technology, several

medically important proteins are now routinely made in bacteria.

– These proteins may prevent or cure a variety of diseases, but they cannot cure inherited disorders—they only treat symptoms.


• Biotechnology may be able to treat inherited disorders in the future.– Patients with defective CFTR proteins in their lung

cells can have viruses containing normal CFTR alleles sprayed into their nose.

– The viruses enter the lung cells, and the normal CFTR allele directs the synthesis of normal CFTR protein.


• Using biotechnology to cure severe combined immune deficiency (SCID)– In the body, new cells are produced from stem cells

that can differentiate into several possible cell types.– SCID is a rare, inherited disorder in which a child fails

to develop an immune system; most die before their first birthday.

– This disorder is due to a defective allele that does not produce an enzyme called adenosine deaminase.


• Using biotechnology to cure severe combined immune deficiency (SCID) (continued)– A 4-year old patient had her white blood cells

treated with a virus containing a functional allele, and these cells were returned to her body.

– Now an adult, she has a normally functioning immune system but must receive continual injections of new treated white cells, since the original treated white cells have died off.

12.7 What Are Some Of The Major Ethical Issues Of Modern Biotechnology?

• Should genetically modified organisms (GMOs) be permitted in agriculture?– Even though transgenic crops offer clear advantages

to farmers, many people strenuously object to transgenic crops or livestock.

– They fear that they may be hazardous to human health or dangerous to the environment.


• Should genetically modified organisms (GMOs) be permitted in agriculture? (continued)– In most cases, there is no reason to think that GMO

foods are dangerous to eat.– The Bt protein is not toxic to mammals, and should

not prove a danger to human health.– However, some people might be allergic to

genetically modified plants.


• Should genetically modified organisms (GMOs) be permitted in agriculture? (continued)– A plant made transgenic by the incorporation of a

new gene may confer upon the crop a trait that induces allergic reactions in some people.

– In 2003, the U.S. Society of Toxicology studied the risks of genetically modified plants and concluded that the current transgenic plants pose no dangers to human health.


• Are GMOs hazardous to the environment?– Bt genes used in rice fields to add herbicide

resistance to the rice may escape in the pollen and enter plants far away from the rice it was intended to control.

– The plants receiving the unintentional genes may then also obtain herbicide resistance.


• Are GMOs hazardous to the environment? (continued)– If these plants are weeds, they will become resistant

to control by the herbicides and will negatively affect the rice crops.

– In 2002, a committee of the U.S. National Academy of Sciences recommended more thorough screening of transgenic plants before they are used commercially, and sustained ecological monitoring after commercialization.


• What about transgenic animals?– Some transgenic animals, such as fish, have the

potential to pose significant threats to the environment.

– If they escaped, they might be more aggressive, grow faster, or mature faster than wild fish, and might replace native populations.

– Commercial fish farms market only sterile transgenic salmon and trout so that escapees would die without reproducing, and thus have minimal effect on the environment.


• Should the genome of humans be changed by biotechnology?– Should people be allowed to select, or even change,

the genomes of their offspring?

parents with genetic disease

fertilizedegg with adefectivegene

embryowith ageneticdefect

therapeuticgenetreated culture

viralvector

baby witha geneticdisorder

Fig. 12-14

therapeuticgene

genetically correctedcell from culture egg cell

withouta nucleus

geneticallycorrectedclone of theoriginal embryo

healthy baby

geneticallycorrectedegg cell

Fig. 12-14


• If it were possible to insert alleles encoding functional CFTR proteins into human eggs, thereby preventing cystic fibrosis, would this be an ethical change to the human genome?

• What about making a bigger and stronger football player?

• When the technology is developed to cure diseases, it will be difficult to prevent it from being used for nonmedical purposes.

12.4 How Is Biotechnology Used In Agriculture?

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