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11-1 The Work of Gregor
Mendel
11-1 The Work of Gregor Mendel
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11-1 The Work of Gregor Mendel
Gregor Mendel’s Peas
Genetics is the scientific study of heredity.
What is heredity?
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11-1 The Work of Gregor Mendel
“Heredity” looks a little like the word “Inherit”.
Heredity is a special type of inheritance – it is why
we look and act somewhat like our parents.
We will be studying genetics (the scientific study
of heredity) for the next several weeks.
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11-1 The Work of Gregor Mendel
Gregor Mendel was an Austrian monk (priest) and
gardner.
His work was important to the understanding of
heredity. Mendel carried out his work with ordinary
garden peas.
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11-1 The Work of Gregor Mendel
Gregor Mendel’s Peas
Mendel knew each
pea plant flower has
both male and female
reproductive parts,
and that:
• the male part of
each flower
produces pollen,
(containing
sperm).
• the female part
of the flower
produces egg
cells.
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11-1 The Work of Gregor Mendel
Pollen grains from a flower on a bee
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11-1 The Work of Gregor Mendel
Gregor Mendel’s Peas
During sexual reproduction in pea plants, sperm (in
pollen) and egg cells join in a process called
fertilization. Fertilization produces a new cell, (and a
new organism), called a zygote.
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Gregor Mendel’s Peas
Since they have both male and female reproductive
parts, pea flowers can be self-pollinating, meaning
they don’t need another pea plant to reproduce.
Sperm cells in pollen fertilize the egg cells in the
same flower.
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The seeds that are produced by self-pollination
inherit all of their characteristics from the single plant
that bore them, because they only have one parent to
get information from.
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11-1 The Work of Gregor Mendel
Gregor Mendel’s Peas
Mendel had true-breeding pea plants that, if allowed
to self-pollinate, would produce offspring identical to
themselves.
True-breeding tall plants would have only tall
offspring, and true-breeding short plants would have
only short offspring.)
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11-1 The Work of Gregor Mendel
Mendel wanted to produce seeds by joining male and
female reproductive cells from two different plants.
He cut away the pollen-bearing male parts of the
plant and dusted the plant’s flower with pollen from
another plant.
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Gregor Mendel’s Peas
This process is
called crosspollination.
Mendel was able
to produce seeds
that had two
different parents.
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11-1 The Work of Gregor Mendel
The offspring of crosses between parents with
different traits are called hybrids.
As an example, for the trait of height, a hybrid plant
can have both tall and short offspring.
A true-breeding plant, the opposite of a hybrid, can
only have plants just like itself.
STOP HERE TODAY
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11-1 The Work of Gregor Mendel
Genes and Dominance
Genes and Dominance
A trait is a specific characteristic that varies from
one individual to another. Some examples of traits
in Mendel’s pea plants are
1)Height (tall or short)
2)Color (green or yellow)
3)Texture (round or wrinkled)
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11-1 The Work of Gregor Mendel
Genes and Dominance
Genes and Dominance
Mendel studied seven pea plant traits, each with two
contrasting characters. (EX: tall and short, round and
wrinkled)
He crossed plants with each of the seven contrasting
characters and studied their offspring.
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Genes and Dominance
Each original pair of plants is the P (parental)
generation.
The offspring are called the F1, or “first filial,”
generation.
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11-1 The Work of Gregor Mendel
The offspring of crosses between parents with
different traits are called hybrids.
As an example, for the trait of height, a hybrid plant
can have both tall and short offspring.
A true-breeding plant, the opposite of a hybrid, can
only have plants just like itself.
STOP HERE TODAY
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11-1 The Work of Gregor Mendel
Mendel was surprised to find that the F1 hybrid plants
all had the character of only one of the parents.
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11-1 The Work of Gregor Mendel
Genes and Dominance
Mendel’s F1 Crosses on Pea Plants
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11-1 The Work of Gregor Mendel
Genes and Dominance
Mendel’s Seven F1 Crosses on Pea Plants
Mendel’s F1 Crosses on Pea Plants
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11-1 The Work of Gregor Mendel
Genes and Dominance
Mendel's first conclusion was that biological
inheritance is determined by factors that are passed
from one generation to the next.
Today, scientists call the factors that determine traits
genes.
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Genes and Dominance
Each of the traits Mendel studied was controlled by
one gene that occurred in two contrasting forms that
produced different characters for each trait.
The different forms of a gene are called alleles (EX:
tall and short are opposite alleles of the same
gene).
Mendel’s second conclusion is called the
principle of dominance.
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11-1 The Work of Gregor Mendel
Genes and Dominance
What is the principle of dominance?
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11-1 The Work of Gregor Mendel
Genes and Dominance
The principle of dominance states that
some alleles are dominant and others are
recessive.
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Genes and Dominance
An organism with a dominant allele for a trait will
always exhibit that form of the trait.(EX a pea plant
may inherit a tall allele from mom, and a short allele
from dad, and the plant will only “show” the tall allele.
That is the plant will be tall.)
An organism with the recessive allele for a trait will
exhibit that form only when the dominant allele for
that trait is not present.
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11-1 The Work of Gregor Mendel
Segregation
What happens during segregation?
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Segregation
Segregation
Mendel crossed the F1 generation with itself to
produce the F2 (second filial) generation.
The traits controlled by recessive alleles reappeared
in one fourth of the F2 plants.
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Segregation
Mendel's F2 Generation
P Generation
Tall
Short
F2 Generation
F1 Generation
Tall
Tall
Tall
Tall
Tall
Short
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Segregation
Mendel assumed that a dominant allele had masked
the corresponding recessive allele in the F1
generation.
The trait controlled by the recessive allele showed up
in some of the F2 plants.
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Segregation
The reappearance of the trait controlled by the
recessive allele indicated that at some point the allele
for shortness had been separated, or segregated,
from the allele for tallness.
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Segregation
Mendel suggested that the alleles for tallness and
shortness in the F1 plants segregated from each
other during the formation of the sex cells, or
gametes.
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Segregation
When each F1 plant flowers and
produces gametes, the two alleles
segregate from each other so that
each gamete carries only a single copy
of each gene.
Therefore, each F1 plant produces two
types of gametes—those with the
allele for tallness, and those with the
allele for shortness.
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Segregation
Alleles separate during gamete formation.
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Gametes are also known as
a. genes.
b. sex cells.
c. alleles.
d. hybrids.
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The offspring of crosses between parents with
different traits are called
a. alleles.
b. hybrids.
c. gametes.
d. dominant.
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In Mendel’s pea experiments, the male gametes
are contained in the
a. eggs.
b. seeds.
c. pollen.
d. sperm.
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In a cross of a true-breeding tall pea plant with a
true-breeding short pea plant, the F1 generation
consists of
a. all short plants.
b. all tall plants.
c. half tall plants and half short plants.
d. all plants of intermediate height.
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If a particular form of a trait is always present
when the allele controlling it is present, then the
allele must be
a. mixed.
b. recessive.
c. hybrid.
d. dominant.
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END OF SECTION