The Ecology Book

35

See also: Early theories of evolution 20–21 ■ Evolution by natural selection 24–31 ■ The rules of heredity 32–33 ■ The

selfish gene 38–39 ■ A system for identifying all nature’s organisms 86–87 ■ Biological species concept 88–89

handling genetic material advance

and we learn more about how

individual genes operate.

Crick and Watson’s breakthrough

was the culmination of decades

of research by numerous scientists,

including Rosalind Franklin and

Maurice Wilkins. While Crick and

Watson worked with 3-D models

to figure out how the components

of DNA fitted together, at King’s

College, London, Franklin and

Wilkins were developing methods of

X-raying DNA to view its structure.

Watson had seen examples of

Franklin’s work that hinted at DNA’s

helical shape shortly before he and

Crick announced their breakthrough.

In 1962 Crick, Watson, and

Wilkins were awarded the Nobel

Prize for Physiology or Medicine.

Franklin, who died in 1958, never

received recognition for her part

in the discovery during her lifetime,

although Crick and Watson openly

acknowledged that her work was

essential to their success.

Double helix structure

DNA is a molecule featuring two

long, thin strands that coil around

each other to resemble a twisted

ladder, in a shape known as a

double helix. Using the ladder

analogy, the sides of the ladder are

made up of deoxyribose (a sugar)

and phosphate, while the rungs

of the ladder consist of paired

nitrogenous bases, adenine (A),

guanine (G), cytosine (C), and

thymine (T). A always pairs up

THE STORY OF EVOLUTION

Genetic engineering

Understanding the structure

of DNA has enabled scientists

to change or “engineer” the

genetic material in cells. It is

possible to cut out a gene from

one organism (the donor) and

place it into the DNA of another

organism. When this practice

was first attempted in the 1970s

it was both difficult and time-

consuming, but technological

advances—such as Clustered

Regularly Interspaced Short

Palindromic Repeats, or CRISPR,

which has been particularly

useful—have greatly simplified

and accelerated the process. In

theory, geneticists can now splice

any gene with any other. They

have attempted some intriguing

combinations, such as the

insertion of the gene for producing

spider silk into goat DNA so

that goats produce milk rich in

proteins. Other substances that

can be produced by modifying

genes are hormones and vaccines.

In gene therapy, a genetically

modified vector (often a virus) is

used to carry a gene into the DNA

of an organism to replace a faulty

or unwanted gene.

A scientist analyzes a sample

of DNA. Genetic manipulation in

medicine is standard practice and

DNA profiling is a vital forensic tool.

with T to form base pair AT, and

G always pairs with C to form

base pair GC.

DNA is the blueprint for life.

Sequences of bases along the

DNA strand constitute the genes

that provide the information that

determines the complete form and

physiology of an organism. A triplet

of bases is known as a codon, and

each codon specifies the production

of one of 20 amino acids; the order

in which the amino acids join

together in a chain determines ❯❯

Molecular biologists James Watson

(left) and Francis Crick (right), pictured

in 1953 with their double helix model

of DNA. Watson called DNA “the most

interesting molecule in all nature.”

DNA is like a computer

program but far, far more

advanced than any

software ever created.

Bill Gates

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