Transcript Mendelian Genetics

Mendelian
Genetics
Biology B/Genetics
Gregor Mendel

Gregor Mendel was a
priest and high school
science teacher who lived
in the 17th century.

Mendel was also in charge
of the garden at the
monastery where he lived.

One of the many plants
that Mendel worked with in
his garden were pea
plants
Pea Plants
 Like many plants, peas use
parts of their flowers to
reproduce:
 The male part of the
flower produces pollen,
which contains male sex
cells
 The female part of the
flower produces eggs,
which are the female sex
cells.
Pea Plants
 There are two ways for pea
plants to reproduce:
 True breeding is when
the flower self pollinates
(asexual reproduction)
 Cross breeding is when
the flower is pollinated by
another flower (sexual
reproduction)
Mendel’s Experiment

Mendel observed that some
of his pea plants were tall,
while others were short.

Height is an example of a
trait, which is a specific
characteristic that varies from
one individual to another.

Mendel decided to study how
this trait got passed from
parent plant to daughter plant
when his pea plants cross
pollinated.
Make A Prediction:

Mendel cross pollinated a
tall and a short pea plant.

He called these plants the
P Generation (P=Parent)

What do you think the
offspring looked like?
The Results:

Much to Mendel’s surprise,
the resulting offspring were
two tall pea plants.

He called these plants the
F1 Generation (F= Filial,
Latin for son)

What happened to the
gene for a short pea plant?
Alleles

Mendel correctly came to
two conclusions:
1.
Inheritance is determined
by genes, which are
factors that are passed
from one generation to
the next. Different forms
of the gene are called
alleles.
Example: The are two alleles
for plant height: tall and
short
The Principle of Dominance
2. An organism with a
dominant allele for a
particular form of a trait
will always have that
form. An organism with a
recessive allele for a
particular trait will have
that form ONLY when the
dominant allele for the
trait is NOT present.
Example: Tall height is
dominant and short
height is recessive.
Punnett Squares

If we use a diagram called a
Punnet Square, we can
understand how Mendel’s
conclusions explained what
happened with the pea
plants:

Both parents were hybrids,
which means that they
carried both the dominant tall
allele AND the recessive
short allele.
Phenotype and Genotype

Phenotype describes the
physical characteristics of an
organism.

Example: If the pea plant is
tall or short.
Genotype describes the makeup of an organism’s genes.

Example: If the pea plant
has two tall alleles, two
short alleles or one tall and
one short allele.
Another Experiment…

Mendel did one more
experiment to test his
theory.

This time he cross
pollinated two tall pea
plants from the F1
Generation.
Make a prediction for the F2
Generation…
The Results

Just as Mendel expected,
this third generation
contained one short and one
tall plant.

Why did the short plant
“reappear”?
…Because the recessive allele
had been “hidden” by the
dominant trait, but was still
present in both parents’
genotypes.
“Hidden” Recessive Alleles
…Because the recessive
allele had been “hidden” by
the dominant trait, but was
still present in both parents’
genotypes.
More Punnett Squares