The Ecology Book

33

Pea plants provided the raw data

that Mendel used to develop his

theories explaining the transmission of

traits from one generation to the next.

See also: Early theories of evolution 20–21 ■ Evolution by natural selection 24–31

■ The role of DNA 34–37 ■ The selfish gene 38–39

THE STORY OF EVOLUTION

(phenotypes) that had only two

distinct forms—for example, white

or purple flowers. When examining

the trait of yellow or green peas,

Mendel took green pea plants and

cross-pollinated them with yellow

pea plants. The peas produced from

this parent generation were all yellow

and Mendel named them the F1

generation. He then cross-pollinated

pea plants from the F1 generation

with each other to produce the F2

generation. He found that some

peas produced were yellow and

some were green. The F1 generation

showed only one trait (yellow), which

Mendel called “dominant.” However,

in the F2 generation 75 percent had

the dominant yellow trait and 25

percent displayed the nondominant

—or “recessive”—green trait.

Laws of inheritance

Mendel theorized that every pea

plant has two factors controlling

each trait. When plants are cross-

pollinated, one factor is inherited

from each plant. A factor can be

dominant or recessive. When both

inherited factors are dominant,

the resulting plant will show the

dominant trait. With a pair of

recessive factors, the plant will

show the recessive trait. However,

if one dominant and one recessive

factor are present, the plant will

show the dominant trait.

Pioneering geneticist

Mendel published his paper in

1866, but no one took much notice

until 1900, when the botanists

Hugo de Vries, Carl Erich Correns,

and Erich Tschermak von

Seysenegg discovered his work.

Scientists then began proving

Mendel’s theories more widely.

Within just ten years, scientists

named the pairs of factors “genes”

and showed that they are linked on

chromosomes. It is now known that

inheritance is far more complex

than Mendel recognized, but his

meticulous research continues to

form the basis for modern studies. ■

Gregor Johann Mendel

Born Johann Mendel in 1822

on a farm in Silesia—then part

of the Austrian Empire and

now in the Czech Republic—

Mendel studied philosophy

and physics at the University

of Olomouc (1840–43). At this

time, he became interested

in the work of Johann Karl

Nestler, who was researching

hereditary traits in plants

and animals. In 1847 Mendel

entered a monastery, where

he was given the name

Gregor. He then went on

to study science further at

Vienna University (1851–53).

When Mendel returned

to his monastery in 1853,

the abbot Cyril Napp gave

him permission to use the

gardens for his research into

hybridization. Mendel himself

became an abbot in 1868 and

no longer had time for his

experiments. Although he

never received credit for his

discoveries during his lifetime,

he is widely regarded as the

founder of modern genetics.

Key works

1866 “Experiments with Plant

Hybrids,” Verhandlungen des

naturforschenden Vereines

in Brünn

Heredity provides

for the modification

of its own machinery.

James Mark Baldwin

American psychologist

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