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Blueprint of Life
Topic 5: Gregor Mendel
Biology in Focus, HSC Course
DOT POINT(s)
 outline the experiments carried out by Gregor Mendel
 describe the aspects of the experimental techniques used
by Mendel that led to his success
Gregor Mendel (1822-84)
Gregor Mendel was an Augustinian monk of Austrian origin. He
also worked as a teacher and an investigator while living in the
monastery in Brünn, Moravia (today this town is Brno in the
Czech Republic).
www.biography.com
Gregor Mendel (1822-84)
He experimented by growing a
variety of garden pea plants and
recording the resulting ratios of
characteristics that appeared in
the offspring. In 1856 he began
his now-famous research and
through his studies he showed
that inherited characteristics are
passed as discrete ‘units’ from
parents to their offspring.
thisgrowinglife.blogspot.com
Gregor Mendel (1822-84)
His choice in garden peas (Pisum
sativum) was critical to his
success as he could easily grow
them in large numbers, they
produced new generations
quickly and had easily
distinguishable characteristics.
He could also control the
population and thus fertilisation
of each flower.
comenius.susqu.edu
Gregor Mendel (1822-84)
Mendel’s breakthrough was that he recognised a pattern in the
inheritance of characteristics by offspring from their parents and
so he proposed a model of inheritance. Using mathematical
calculations, he was able to predict the ratios of various types of
offspring from any two specific parents.
blog.scs.sk.ca
Gregor Mendel (1822-84)
This work led him to formulate
principles of inheritance which held
up to testing and later became
known as Mendel’s laws. These laws
are applied universally today to
describe patterns of heredity and
variation in living organisms, a field
of biology known as genetics.
Mendel’s work marked the start of
this branch of biology and so Mendel
is referred to as the ‘father of
genetics’.
www.myspace.com
Gregor Mendel (1822-84)
Mendel was working on inheritance in garden peas at the same
time that Charles Darwin was writing up his theory of evolution
(from results that he had collected over many years) and Alfred
Wallace was developing his theory of evolution.
Gregor Mendel (1822-84)
Both Darwin and Wallace were unaware of Mendel’s work at the
time. Mendel was aware of Lamarck’s (he was the first scientist to be
widely acknowledged for a theory regarding evolution) proposal and
there is evidence that Mendel had read a copy of Darwin’s book in
1860 (after Mendel had completed his investigations, but before he
wrote his own papers).
www.corkfpc.com
Gregor Mendel (1822-84)
However, Mendel did not seem to
make any links between his work
and that of Darwin. This is not too
surprising if one considers that
Mendel’s work at that stage related
to garden pea plants only—his
work on the inheritance of
characteristics in general was only
later applied to other organisms,
resulting in the development of
universal laws of inheritance.
thisgrowinglife.blogspot.com
Mendel’s Experiments
Mendel experimented with garden pea plants, investigating their
breeding patterns to determine the inheritance of characteristics
(traits). Pea plants were ideally suited because they can be easily
grown and cross-bred, have a short life cycle (they are annual
plants) and both male and female parts are present in their
flowers.
www.flowersinisrael.com
Mendel’s Experiments
The traits he studied were:
 stem length: tall or short
 the colour of the seed contents: yellow or green
 the colour of seed coat: grey or white
 the shape of the seed: round or wrinkled peas
 the colour of the unripe pod: yellow or green
 flower position: axial or terminal
 pod shape: inflated or constricted.
world.edu
Mendel’s Experiments
Mendel studied the inheritance of each trait individually (e.g. trait
= stem length), investigating the inheritance of one pair of
contrasting features at a time (e.g. tall or short stem length).
www.takdangaralin.com
How Mendel Studied The Traits
Over a period of 2 years, Mendel
established pure-breeding lines of
pea plants which he then crossbred
to study the inheritance of their
characteristics (traits). At the time,
it was believed that if parents with
contrasting characteristics for a
particular feature were crossed, the
offspring would display a ‘blending’
of the characteristics. For example
if a tall plant and a short plant were
crossed, the expected offspring
would be of medium height.
www.exploringnature.org
How Mendel Studied The Traits
When Mendel experimentally tested this hypothesis, he obtained
quite different and unexpected results—all of the initial offspring
resembled one parent, but in later generations the other parent’s
trait would arise, appearing to have ‘skipped a generation’. From
his direct counts of resulting plants, Mendel developed
mathematical ratios that provided evidence for what are today
known as Mendel’s laws.
www.softchalk.com -
How Mendel Studied The Traits
Mendel’s laws:
■ Mendel’s law of dominance and segregation
■ Mendel’s law of independent assortment.
www.dipity.com
How Mendel Studied The Traits
For the purposes of the HSC
curriculum, we will study in detail
Mendel’s first law of dominance and
segregation, developed as a result of
his study of monohybrid crosses.
Mendel’s second law of independent
assortment is based on dihybrid
crosses and will only be dealt with in
detail in the optional module,
‘Genetics: the code broken?’. We
may or may not chose to study this.
www.rentmidwest.com
Mendel’s Experimental Techniques
Mendel used sound scientific
experimental technique—he
carried out well-controlled
experiments from which he
gathered quantitative data to
arrive at valid conclusions.
www.radio.cz
Mendel’s Experimental Techniques
Mendel controlled the breeding lines of his experiments in the
following way:
 To ensure pure-breeding lines: over a period of 2 years, Mendel
established pure-breeding lines. He ensured that the pea plants
would self-pollinate by using plants with flowers that had both
male and female parts enclosed within one flower.
12knights.pbworks.com
Mendel’s Experimental Techniques
These were kept isolated in a greenhouse, to prevent accidental
cross-pollination. Mendel bred tall parent plants that gave rise to
only tall offspring and short parent plants that gave rise to short
offspring, both over several generations.
mendel.devildream.com
Mendel’s Experimental Techniques
Using hundreds of pea plants, Mendel manually transferred pollen,
e.g. from the anthers of tall plants to the stigmas of short plants
(which had no stamens, to prevent accidental selfpollination).
world.edu
Mendel’s Experiment in Detail
1. He established 2 pure breeding lines: 1 tall and 1 short. He did
this by using male and female parts within the same flower. The
offspring of pure-breeding lines all resemble their parents,
ensuring that they in turn are pure-breeding for a particular trait
(characteristic). The resulting tall or short offspring that are ‘purebred lines’ become the P or parent generation in subsequent
crosses.
www.emc.maricopa.edu
Mendel’s Experiment in Detail
2. Mendel then created hybrids by cross-bred two plants with
contrasting pure-bred characteristics—tall × short. He manually
transferred pollen between tall and short plants (controlled by
removing anthers of recipients)
world.edu
Mendel’s Experiment in Detail
When parents that are purebreeding for contrasting
characteristics (such as tallness
and shortness) are crossed, the
offspring all resemble one parent
(in this case, the tall parent).
world.edu
Mendel’s Experiment in Detail
These offspring (the F1 or first
filial generation) are termed
hybrids (mixed breeds), but they
resemble only one parent.
Mendel called the characteristic
of the parent that they resemble
dominant and the other
characteristic, which is masked,
recessive. In this cross, ‘tall’ is
dominant over ‘short’
(recessive).
world.edu
Mendel’s Experiment in Detail
3. Mendel carried out a
monohybrid cross by cross-breeding
two F1 individuals that are hybrid
for one particular trait. In other
words, two hybrid plants from the
first filial generation of the previous
experiment. Some were allowed to
undergo selfpollination, whereas
others were crosspollinated,
because all were hybrids; a large
sample size was used.
world.edu
Mendel’s Experiment in Detail
When two hybrid plants are
crossed, one characteristic
(dominant) appears three times as
frequently in the offspring as the
other (recessive) characteristic.
That is, the average ratio observed
in offspring is 3:1. It appears that
one factor that was passed down
from the original parent
generation became ‘masked’ or
hidden in the F1 generation and
then reappeared in the F2
generation.
world.edu
Mendel’s Experiment in Detail
4. Mendel derived principles
based on mathematical
calculations. He showed that
these ratios arise if an individual
possesses two ‘factors’ for any
characteristic, where one is
dominant over the other, and
these two factors segregate or
separate when they are passed
from parent to offspring.
world.edu
Mendel’s Experiment in Detail
Mendel proposed that during
reproduction, the two factors
segregate and each passes into a
separate gamete. When two
gametes combine during
fertilisation, each contributes
one factor to the newly formed
offspring. Mendel used statistics
to calculate the probability of
different combinations of factors
pairing in offspring and he
obtained a 3:1 ratio.
world.edu
Mendel’s Experiment in Detail
5. Mendel made direct counts of the resulting offspring, giving
quantitative data, which he collated and analysed to identify
patterns and trends. Mendel applied logical thinking and a
mathematical model to the data he had gathered, leading to his
valid conclusions.
www.flickr.com
Mendel’s Experiment in Detail
He used a mathematical model
to explain the phenomenon of
inheritance and to make
predictions for future crosses
(which he later tested
successfully). He justified all of
his inferences and conclusions—
his ratios provided supporting
evidence for the establishment of
his universal laws.
www.biography.com
Activity
-Handout Table 2.1 which outlines Mendel’s experiments