Biology 12

CHAPTER

9

Reflecting

Questions

DNA Mutations and

Genetic Engineering

284

Much of what you have learned

about genetics so far treats hereditary

information as being relatively

stable. You have probably learned,

for example, that brown eyes are

dominant and blue eyes are recessive,

and that these traits are passed

from parents to their offspring in a

statistically predictable way. But if

this is always so, how do you explain

the appearance of this adult dog?

Why doesn’t the adult dog have

either brown eyes or blue eyes?

In reality, the genome of any

organism is far from stable. In the

dynamic environment of the cell,

the structure of DNA is constantly

changing. Single nucleotide bases

and entire genes are copied, shuffled,

lost, and regained. Modifications in

regulatory sequences activate some

genes and silence others. Stretches

of nucleotides “jump” from one

chromosome to another. Within a

single organism, changes like these

produce such diverse results as an

unusual eye colour or a cancerous

tumour. As genetic changes are passed

down over generations, they give rise

to all the diversity of living organisms.

In the natural world, molecular

changes in DNA are largely

unpredictable, usually harmful if

inherited, and infrequently passed

from one species to another. In the

laboratory, these natural barriers are

breached. What happens, for

example, when you mix bacterial,

plant, and human DNA? If you follow

the right recipe, you might create the

corn plant shown here, which was

engineered to produce a human

antibody that fights cancer. Such

“plantibodies” are only one example

of the uses of a growing number of

genetically engineered organisms.

These organisms offer society benefits

in such fields as medicine, agriculture,

and the environment, but they may

also come with significant risks.

In this chapter, you will learn about

the kinds of changes that can occur

in genetic material. You will examine

the processes involved in genetic

technologies to see how genetic

material can be deliberately

manipulated by researchers, and you

will tackle some of the difficult moral

and ethical questions that arise from

activities such as DNA sequencing,

genetic engineering, gene therapy,

and cloning.

Genetic engineering can transform

a corn plant into a source of human

antibodies. Even in the natural

world, the structure of DNA is

constantly in flux.

In what ways can

substances in the external

environment alter the

information contained

in DNA within a cell?

How can scientists change

the structure of DNA to

produce new kinds of

organisms?

What are some of the

benefits and risks of

genetic engineering?

Prerequisite

Concepts

and Skills

Before you begin this chapter,
review the following concepts
and skills:

comparing nucleotide

sequences to the

polypeptide product

of a gene (Chapter 8,

section 8.1),

describing the process

of complementary base

pairing in the DNA

molecule (Chapter 7,

section 7.2),

summarizing the

processes and enzymes

involved in DNA

replication and

proofreading (Chapter 7,

section 7.3), and

outlining the main

pathways for gene

expression and regulation

in living cells (Chapter 8,

section 8.4).