Aim: What were the contributions of
Gregor Mendel to the study of
genetics?
The Work of Gregor Mendel
Genetics: the scientific study of heredity,
or how traits are passed from one
generation to the next
Gregor Mendel’s Peas
- Mendel was an Austrian monk who is
credited as the “father of genetics.”
The Work of Gregor Mendel
- Mendel began working with pea plants
that were true-breeding, meaning
that if allowed to self pollinate, they
would only produce offspring identical
to themselves
-ex. Tall plants produce tall plants,
green seeded plants produce green
seeded plants
The Work of Gregor Mendel
Genes and Dominance
- Mendel studied 7 different plant
traits. Traits are characteristics such
as height or flower color.
The Work of Gregor Mendel
Seed
Shape
Round
Wrinkled
Round
Seed
Color
Yellow
Green
Yellow
Seed Coat
Color
Gray
White
Gray
Pod
Shape
Smooth
Constricted
Smooth
Pod Color
Flower
Position
Green
Axial
Yellow
Green
Terminal
Axial
Plant Height
Tall
Short
Tall
The Work of Gregor Mendel
- Mendel called the original plants the P
(parent) generation. The offspring
were the F1 (first filial) generation .
- the offspring of crosses between
parents of different versions of the
same trait are called hybrids
The Work of Gregor Mendel
Mendel's F2 Generation
P Generation
Tall
Short
F2 Generation
F1 Generation
Tall
Tall
Tall
Tall
Tall
Short
11-1 The Work of Gregor
Mendel
From his experiments, Mendel drew two
conclusions
1) biological inheritance is determined
by factors that are passed from one
generation to the next. Today we call
these factors genes.
- the different forms of a gene are
called alleles
The Work of Gregor Mendel
Example: Trait – Ear lobe position
Allele – attached or free
2) the second conclusion is called the
principle of dominance
- the principle of dominance states that
some alleles are dominant (or
expressed) and others are recessive
(not expressed- hidden)
The Work of Gregor Mendel
Segregation
- Mendel saw that some forms of traits
would disappear during the F1
generation, but reappear during the F2
generation
- he explained this by showing that the
alleles segregated during the
formation of gametes, or sex cells.
The Work of Gregor Mendel
Section Quiz
Gametes are also known as




genes.
sex cells.
alleles.
hybrids.
Section Quiz
The offspring of crosses between parents with
different traits are called




alleles.
hybrids.
gametes.
dominant.
Section Quiz
In a cross of a true-breeding tall pea plant with a
true-breeding short pea plant, the F1 generation
consists of
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
all short plants.
all tall plants.
half tall plants and half short plants.
all plants of intermediate height.
Section Quiz
If a particular form of a trait is always present
when the allele controlling it is present, then
the allele must be




mixed.
recessive.
hybrid.
dominant.
Probability and Punnett
Squares
Genes and Probability
- the likelihood that an event will occur is
called probability
ex. a coin landing on heads has a
probability of 50%
- the principle of probability can be used
to predict the outcome of genetic crosses
Probability and Punnett
Squares
Punnett squares
- the gene combinations that might
result from a genetic cross can be
determined by drawing a diagram
known as a Punnett square
Probability and Punnett
Squares
Probability and Punnett
Squares
Organisms that have two identical alleles
for a particular trait are called
homozygous (true-breeding).
ex. TT
Organisms that have two different alleles
for a particular trait are called
heterozygous (hybrid)
ex. Tt
Probability and Punnett
Squares
Probability and Punnett
Squares
The physical characteristics of an
organism are called its phenotype
ex. tall plant
The genetic makeup of an organism is its
genotype
ex. TT or Tt
Section Quiz
Probability can be used to predict
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average outcome of many events.
precise outcome of any event.
how many offspring a cross will produce.
which organisms will mate with each other.
Section Quiz
Compared to 4 flips of a coin, 400 flips of the coin
is




more likely to produce about 50% heads and 50%
tails.
less likely to produce about 50% heads and 50%
tails.
guaranteed to produce exactly 50% heads and 50%
tails.
equally likely to produce about 50% heads and 50%
tails.
Section Quiz
Organisms that have two different alleles for a
particular trait are said to be




hybrid.
heterozygous.
homozygous.
recessive.
Section Quiz
Two F1 plants that are homozygous for shortness
are crossed. What percentage of the offspring
will be tall?




100%
50%
0%
25%
Exploring Mendelian
Genetics
Independent assortment
- The principle of independent assortment
states that genes for different traits can
segregate independently during the formation
of gametes.
example: Seed color does not depend on seed
shape
- In order to test his hypothesis, Mendel
conducted a dihybrid cross.
Independent assortment
•
In one dihybrid cross experiment, Mendel studied
the inheritance of seed color and seed shape.
•
•
•
The allele for yellow seeds (Y) is dominant to the
allele for green seeds (y).
The allele for round seeds (R) is dominant to the
allele for wrinkled seeds (r).
Mendel crossed true-breeding plants that had
yellow, round seeds (YYRR) with true-breeding
plants that has green, wrinkled seeds (yyrr).
Exploring Mendelian
Genetics
Summary
•
•
•
The independent assortment of each pair of alleles
during gamete formation is now called Mendel’s
law of independent assortment.
Mendel was very lucky!! He happened to
study seven traits of the pea plant that, in fact,
did sort independently.
Not all traits are inherited independently.
Certain traits are linked, such as sexual
characteristics.