11 déc. 2012 (il y a 8 années et 7 mois)

325 vue(s)


Chapter 10


Golden Rice or Frankenfood?

Genes from one species may be inserted into an individual of another species

or a
gene may be modified and reinserted into an individual of the same species

Golden Rice

Rice plan
ts with added genes make and store beta carotene


An organism that has been genetically modified with genes from a different species

Genetically modified organisms


Organism whose genome has been modified by genetic engineering

10.2 F
inding Needles in Haystacks

Gene research was limited until enzymes produced by bacteria to cut viral DNA were

Restriction enzyme

Enzyme that cuts DNA at specific base sequences

Used in DNA cloning to cut DNA into pieces that are inserted into

cloning vectors

DNA Cloning

DNA cloning mass
produces DNA fragments for research

DNA cloning

Set of procedures that uses living cells to make many identical copies of a DNA


A genetically identical copy of DNA, a cell, or an organism

ning Vectors

Cloning vector

A DNA molecule that can accept foreign DNA, resulting in a hybrid molecule that
can be transferred to a host cell, and get replicated in it


A small, circular DNA molecule in bacteria, replicated independently of the

A cloning vector

Recombinant DNA

Recombinant DNA molecules are introduced into host cells such as bacteria, which
copy the DNA as they divide

Recombinant DNA

Contains genetic material from more than one organism

Making Recombinant DNA

1. A rest
riction enzyme recognizes specific base sequences in DNA from two different

2. Restriction enzymes cut DNA into fragments with single
stranded tails (“sticky ends”)

3. DNA fragments from different sources are mixed together; matching sticky ends ba

4. DNA ligase joins fragments, forming recombinant DNA

Commercial Plasmid Cloning Vector

cDNA Cloning

RNA cannot be cloned directly; reverse transcriptase is used to copy single
RNA into cDNA for cloning

Reverse transcriptase

Viral enz
yme that uses mRNA as a template to make a strand of DNA


DNA synthesized from an RNA template by the enzyme reverse transcriptase


A library is a collection of cells that host different fragments of DNA, often
representing an organism’s ent
ire genome

Researchers make DNA libraries to isolate one gene from the many other genes in a


An organism’s complete set of genetic material

Nucleic Acid Hybridization

Probes are used to identify one clone that hosts a DNA fragment of intere
st among
many other clones in a DNA library


Short fragment of DNA labeled with a tracer

Hybridizes with a specific nucleotide sequence

Nucleic acid hybridization

pairing between DNA or RNA from different sources


PCR quickly mass
copies of a particular DNA fragment for study

Polymerase chain reaction (PCR)

Uses primers and heat
resistant DNA polymerase to rapidly generate many copies
of a DNA fragment


Short, single
strand of DNA designed to hybridize with a DNA fragment

teps in PCR

1. Starting material is mixed with DNA polymerase, nucleotides and primers

2. Mixture is heated and cooled in cycles

At high temperature, DNA unwinds

At low temperature, primers base
pair with template DNA


polymerase synthesizes compleme
ntary DNA strands on templates

10.3 Studying DNA

Short tandem repeats are multiple copies of a short DNA sequence that follow one
another along a chromosome

The number and distribution of short tandem repeats, unique in each individual, is
revealed by el
ectrophoresis as a DNA fingerprint

DNA Fingerprinting

DNA fingerprinting is used in forensics, court evidence, and other applications

DNA fingerprint

An individual’s unique array of short tandem repeats


Used to separate DNA fragments by

The Human Genome Project

Automated DNA sequencing and PCR enabled scientists to sequence the more than 3
billion bases of the human genome


Method of determining the order of nucleotides in DNA

Sequencing a Fragment of DNA

The order of co
lors is the order of DNA bases (A, T, G, C)


Analysis of the human genome sequence is yielding new information about human
genes and how they work


The study of genomes (structural genomics, comparative genomics)

10.4 Genetic Engineerin

Recombinant DNA technology and genome analysis are the basis of genetic

Genetic engineering is the directed alteration of an individual’s genome, resulting in a
genetically modified organism (GMO)

Genetic engineering

Process by which deliber
ate changes are introduced into an individual’s genome

Genetically Modified Microorganisms

A transgenic organism carries a gene from a different species

Transgenic organisms are used in research, medicine, and industry

Transgenic bacteria and yeast produc
e medically valuable proteins

Designer Plants

Transgenic crop plants help farmers produce food more efficiently

Plants with modified or foreign genes are now common in farm crops

Using the Ti plasmid

to Make a Transgenic Plant

Animation: Gene transfer
using a Ti plasmid

Genetically Modified Crops


gene confers insect resistance to corn

Biotech Barnyards

Transgenic animals produce human proteins

Animals that would be impossible to produce by traditional breeding methods are
being created by genetic


Transgenic animals are used in research, medicine, and industry

Transgenic Animals

Knockout Cells and Organ Factories

Transgenic animals may one day provide a source of organs and tissues for
transplantation into humans


Transplant of an organ from one species to another

10.5 Genetically Modified Humans

Genes can be transferred into a person’s cells to correct a genetic defect or treat a

However, the outcome of altering a person’s genome remains unpredictable

e therapy

Transfer of a normal or modified gene into an individual with the goal of treating a
genetic defect or disorder

Unpredictable Outcomes

There are more than 15,000 serious genetic disorders

gene therapy is the only real

In some cases, gene

therapy works

in other cases it leads to death

Inserting a virus
injected gene into a chromosome can disrupt normal function and
cause cancer

Severe allergic reaction to the viral vector can cause death

One Successful Case of Gene Therapy

Rhys Evans,
born with a severe immune disorder (SCID
X1) received a normal gene
and no longer lives in isolation

Getting Perfect


Idea of deliberately improving the genetic qualities of the human race

The potential benefits of genetically modifying humans mus
t be weighed against the
potential risks, including social implications



Golden rice with beta carotene was ready for distribution in 2005 but is still not
available for human consumption

the biosafety experiments required a
re too
expensive for the public humanitarian agency that developed it