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Chapter 11: Intro to Genetics
11-1
The Work of Gregor Mendel
Intro
• What is an inheritance?
• Money or property left
behind from a relative who
has passed away.
• Another form of inheritance
has to do with your GENES!
• Every living thing has a set
of characteristics inherited
from its parents or parent.
• What is the scientific
study of heredity called?
• Genetics
Gregor Mendel’s Peas
• Who was Gregor Mendel?
• An Austrian monk who
studied biological
inheritance.
• Born in 1822 in what is
now the Czech Republic.
• After becoming a priest,
spent several years
studying math and science.
• Spent 14 teaching at the
monastery high school. He
was also in charge of the
garden there. It was here
that he did experiments
with garden peas.
Gregor Mendel’s Peas
• What did Gregor
Mendel know about
these pea plants?
• Part of each flower produces
pollen, which contains the
plants male reproductive cells
or sperm.
• The female portion of the
flower produces eggs.
• During sexual repro, male &
female repro cells in a process
called fertilization.
• Fertilization produces a new
cell which develops into an
embryo encased in a seed.
Gregor Mendel’s Peas
• How do pea flowers
reproduce?
• They are self-pollinating,
meaning that sperm cells in
pollen fertilize the egg cells in
the same flower.
• The seeds produced by selfpollination inherit all of their
characteristics from the single
plant that bore them. They
have a single parent.
• When Mendel took charge of
the monastery garden, he had
true breeding plants. This
means that if they were
allowed to self-pollinate, they
would produce offspring
identical to themselves.
Pollination
• Pea Flower (selfpollination)
• Cross Pollination
•
Mendel’s Experiments
• What did Mendel want
to do?
• Mendel wanted to produce
seeds by joining male &
female repro cells from 2
different plants- (cross
pollination). First he had to
prevent self-pollination.
• To do this, he cut away the
male parts and dusted
pollen from another plant
onto the flower.
• Produced seeds from 2 diff
parents. This allowed
Mendel to cross breed &
study the traits.
Genes and Dominance
• How many traits did
Mendel Study?
• What is a trait?
• He studied 7 different
traits on the pea plants.
• A specific
characteristic (seed
color, plant height)
that varies from 1
individual to another.
Genes and Dominance
• When describing plants
what does “P” mean?
• What does the “F1”
represent?
• The original pair of plants
or the “parental”
generation.
• The offspring or “first
filial.”
• Filius and filia are the
Latin words for son &
daughter.
• The offspring of crosses
between parents with
different traits are called
hybrids.
Genes and Dominance
• What were Mendel’s
results? Did the
characteristics of the
parents blend in the
offspring?
• Not at all. All of the
offspring had the
characters of only one
of the parents.
• In each cross, the
character of the other
parent seemed to
disappear.
Genes and Dominance
• What were Mendel’s
conclusions? (There were
two conclusions).
• What are different forms a
gene called?
• 1st: Biological inheritance is
determined by factors that are
passed from 1 generation to the
next. Today these “factors” are
called genes.
• Each of the traits Mendel
studied was controlled by 1
gene that occurred in two
contrasting forms. Ex: height:
short and tall
• They are called alleles (uhLEELZ)
Genes and Dominance
• 2nd: Principal of
Dominance
– Some alleles are dominant
& others are recessive.
– Dominant allele will always
be displayed.
– Recessive allele will only
be displayed when the
dominant form is not
present.
– Mendel’s Exp: Tall
(dominant), short recessive;
yellow (dominant), green
(recessive)
Segregation
• How had the recessive
alleles disappeared in
Mendel’s
experiments? Or were
they still present in the
F1 plants?
• To answer this
question, Mendel
allowed all 7 kinds of
F1 hydrid plants to
produce an F2 (second
filial) generation by
self pollination.
• He X the F1 generation
with itself to produce
the F2 offspring.
Segregation
• What did Mendel
observe?
• When Mendel
compared the F2
plants, he found that
the traits controlled by
the recessive alleles
reappeared! (1/4)
Explaining the F1 Cross
• Why did the recessive
alleles seem to
disappear in the F1
and then reappear in
the F2?
• Mendel assumed that the
dominant allele masked
the recessive allele.
However, the recessive
allele showed up in some
of the F2 plants.
• At some point the allele
for tallness had been
separated from the allele
for shortness.
Explaining the F1 Cross
• How did this
segregation occur?
• Mendel suggested that
these alleles
segregated from each
other during the
formation of gametes
(GAM-eetz), or sex
cells.
Explaining the F1 Cross
• What happens to the
alleles during
segregation?
• When each F1 plant
flowers and produces
gametes, the 2 alleles
segregate from each other
so that each gamete carries
only a single copy of each
gene. Therefore, each F1
plant produces 2 types of
gametes, those with the
allele for tallness and
those with the allele for
shortness.
Alleles segregate and are then paired up again when the
gametes fuse during fertilization. Capital “T” represents
the dominant allele. Lower case “t” represents the
recessive allele. The F2 gen has a new combo of alleles.