Download During the 1860` s, an Austrian monk and biologist named Gregor

During the 1860' s, an Austrian monk
and biologist named Gregor Mendel worked
among hundreds of pea plants in the garden of
a small monastery in Czechoslovakia. Mendel
experimented with pea plants to seeif he could
fmd a pattern in the way certain characteristics
are handed down from one generation of pea
plants to the next generation. Another word for
the characteristics of an organism is trait. So
Mendel actually studied the way certain traits
are passedon from one generation of organisms
to the next generation. Pea plant traits include
how tall the plant grows, the color of their
seeds,and the shape of their seeds.
Although Mendel 4id not realize it at
the time, his experiments would come to be
consideredthe beginning of genetics. Genetics
is the study ofheredity, or the passing on of
traits from an organism to its offspring. F or
this reason, Mendel is called the Father of
Genetics.
Mendel chose pea plants for his
experiments becausepea plants grow and
reproduce quickly. So he knew that he could
study many generations of pea plants in a short
amount of time. Mendel also knew that pea
plants had a variety of different traits that could
be studied at the sametime. That is, he could
study plant height, plant seed color, plant seed
shape and other traits in the sameexperiment.
At first, Mendel was bewildered by the
behavior of certain traits of pea plants. For
example, when he grew pea plant from seeds
produced by certain tall pea plants that he had
pollinated with pollen from short pea plants,
Mendel expected all of the offspring to be of
medium height. Instead, all of the offspring
were tall. Every time he repeatedthis procedure
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These pea plants display the ideal ratio of tall to short plants for offspring
of parents that each had a dominant
and recessive gene for height.
with the same plants, he got the same results. It
seemedthat there was something about the tall
trait that overwhelmed, or dominated, the short
trait. Mendel called this stronger trait the
"dominate trait." He called the trait that was
dominated the "recessive trait," becauseit
seemedto recede, or vanish.
Mendel then decided to try something
different. He took a group of the tall offspring
and cross pollinated them. He harvested the
seedsand replanted them. Surprisingly, he
found some short pea plants among the
offspring. Mendel detected a pattern to his
results that helped him to recognize some of the
fundamental principles of heredity.
Mendel was convinced that the male
and the female pea plant each contributed
something during fertilization that helped
determine a trait. Since each parent contributed
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something, he concluded that there had to be a
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for
be talloi --,
that these ..somethings"
that Mendel observed in
are each determined by a pair of
genes -one gene from the male and one from
the female.
Mendel used upper caseletters to
represent the dominant gene. For example, he
used '.r' as the symbol for the tallness gene in
pea plants. He used a lower case.'t" as the
symbol for shortness in pea plants. Mendel
believed that whenever an organism expresses,
or displays, a dominant trait, at least one
dominant gene must be present,F or example, if
a pea plant is tall, its gene pair has to be either
'.TT" or "Tt."