The Science Book

326

See also: Gregor Mendel 166–71 ■ Thomas Hunt Morgan 224–25 ■

James Watson and Francis Crick 276–83

C

loning is the production of

a new, genetically identical

organism from a single

parent. It occurs in nature, such as

when a strawberry plant sends out

runners and the offspring inherit all

their genes asexually. However,

artificial cloning is tricky, as not

all cells have the potential to grow

into complete individuals, and

mature cells may be reluctant to do

so. The first successful cloning of a

multicell organism was achieved

in 1958 by British biologist

F. C. Stewart, who grew a carrot

plant from a single mature cell.

Cloning animals proved trickier.

Cloning animals

In animals, fertilized eggs and the

cells of a young embryo are among

the few totipotent cells—cells that

can grow to form a whole body. By

the 1980s, scientists could produce

clones by separating young embryo

cells, but it was difficult. British

biologist Ian Wilmut and his team

instead inserted the nuclei of body

cells into fertilized eggs that had

had their genetic material removed—

thereby making them totipotent.

Using udder cells of sheep as

the source of nuclei, the team

inserted the resultant embryos into

sheep to develop normally. In total,

27,729 of these cells grew into

embryos, and one, named Dolly,

born in 1996, survived into

adulthood. Research into cloning

for agriculture, conservation,

and medicine continues, as does

public debate over its ethics. ■

A NEW LAW

OF NATURE

IAN WILMUT (1944–)

IN CONTEXT

BRANCH

Biology

BEFORE

1953 James Watson and

Francis Crick demonstrate

that DNA has a double helix

structure that carries the

genetic code and can replicate.

1958 F. C. Stewart clones

carrots from mature

(differentiated) tissues.

1984 Danish biologist Steen

Willadsen develops a way of

fusing embryo cells with egg

cells that have had their

genetic material removed.

AFTER

2001 The first endangered

animal, a gaur (Indian bison)

named Noah, is born in the US

by reproductive cloning. It dies

of dysentery two days later.

2008 Therapeutic cloning of

tissue is shown to be effective

at curing Parkinson’s disease

in mice.

The pressures for human

cloning are powerful;

but we need not assume

that it will ever become a

common or significant feature

of human life.

Ian Wilmut