Download Mendel and the Pea Plants

Mendel and the Pea Plants
The laws of genetics
Introduction to the lesson
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Vocabulary page
Introduction
The cutting edge of science
is genetics. From a few
drops of blood scientist can
test for all sorts of diseases
and treat many of them. But
the study of genetics is not as new as you
would assume. In fact, the study of
genetics was started in the 19th century (1800s) by a
monk named Gregor Mendel.
Mendel’s work


Mendel was not a famous scientist.
Instead he was a monk and a lowly
science teacher who was naturally
curious. He became the father of
genetics by accident.
Mendel started experimenting with
pea plants for the fun of it. He did
not set out to found a new field of
study.
Mendel’s work

Mendel studied pea plants for two
reasons



He could control the plant’s pollination
Many of the plant’s traits had two
possibilities and were very easy to see.
He worked for seven years and
performed thousands of
experiments before he came up
with his laws of segregation.
Mendel’s work



Mendel’s first experiments used two true
breeding plants that differed by only one
trait. This is called a monohybrid cross.
He observed that one of the traits seen in
the true breeding parents disappeared in
the first generation but reappeared in the
second generation in a predictable ratio.
From these experiments Mendel made 4
hypotheses.
Mendel’s hypotheses


There are multiple forms of genes
called alleles.
An organism has two alleles for
each gene. They receive 1 allele
from each parent. If the two alleles
are the same, the organism is
Homozygous. If the two alleles are
different, the organism is
Heterozygous
Mendel’s hypotheses


When only one of the two different alleles
in a in a heterozygous individual appears
to affect the trait, that allele is called the
dominant allele. In such cases, the other
allele that does not appear to affect the
trait is called the recessive allele.
The two alleles for a character separate
during the formation of gametes, so that
each gamete carries only one allele for
each character.
Pea characteristics

Mendel studied 7 characteristics of
the pea plant. For each one he
found a dominant trait and a
recessive trait as his third
hypothesis says.
Pea characteristics







Purple flowers are dominant over white
flowers
Axial flower position is dominant over
terminal flower position
Yellow seeds are dominant over green seeds
Round seeds are dominant over wrinkled
seeds
Green seed pods are dominant over yellow
pods
Inflated pods are dominant over constricted
pods
Tall plants are dominant over dwarf plants
Probability of a monohybrid cross


When Mendel made a monohybrid cross he
found that one trait disappeared in the first
generation (the recessive trait) and
reappeared in the next generation predictable
ratio.
Mendel found that one plant out of four would
have the recessive trait and that three plants
out of four would have the dominant trait
when he crossed the offspring of two true
breeding plants that differed by the one
characteristic being studied.
Looks versus Genetics



Something was different between the true
breeding dominant plant and the first
generation dominant plants. They looked the
same but the first generation plants could
produce a recessive plant and the true
breeding plants could not. WHY?
The way a plant looks is called its Phenotype.
Two plants can look the same but have
different genetics like our Monohybrid
example.
A plant’s genetics for a trait is called its
Genotype. This is what alleles the plant has
for the trait in question.
Looks versus Genetics
How can you tell the difference?


Here is the next question. If a plant
has the dominant Phenotype how can
you tell what the Genotype is? The
answer: You do a test cross.
To do a test cross you cross a true
breeding recessive plant with the
dominant plant in question and look
at the offspring.
Test cross offspring.


If you have only dominant offspring
the genotype for the plant in
question is Homozygous dominant.
If you have dominant and recessive
offspring the genotype for the plant
in question is Heterozygous
dominant.
Lesson Review


Now that you have read the basic
principles of genetics let’s see how
well you remember them
On the following slides are True and
False questions about genetics.
Click on the square beside the best
answer for the question to see if
you are right.
Lesson Review
1. The field of genetics started in the
1900s
True
False
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correct. Click on the house button
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answer. Please
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next question
Lesson Review
2. Gregor Mendel was a monk, a
teacher and the father of genetics
True
False
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correct. Click on the house button
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answer. Please
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next question
Lesson Review
3. Gregor Mendel studied the pea
plant because he could control the
pollination and he could easily see
the different traits
True
False
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correct. Click on the house button
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answer. Please
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next question
Lesson Review
4. Monohybrid crosses examine plants
that are exactly the same except for
one trait.
True
False
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correct. Click on the house button
to go back and review the lesson.
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the quiz.
Correct
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answer. Please
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next question
Lesson Review
5. There are multiple forms of genes
called alleles
True
False
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correct. Click on the house button
to go back and review the lesson.
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the quiz.
Correct

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answer. Please
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next question
Lesson Review
6. A homozygous plant has two
alleles for a characteristic that are
the same.
True
False
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correct. Click on the house button
to go back and review the lesson.
Click on the arrow to continue with
the quiz.
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answer. Please
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next question
Lesson Review
7. Mendel studied 3 traits of the pea
plant.
True
False
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correct. Click on the house button
to go back and review the lesson.
Click on the arrow to continue with
the quiz.
Correct
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answer. Please
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next question
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Vocabulary
Allele - alternative form of a gene
Dominant - descriptive of an allele in a heterozygous individual
that appears to be the only one affecting a trait
Genotype - genetic makeup of an organism; an organism's
combination of alleles
Heterozygous - having different alleles for a gene
Homozygous - having identical alleles for a gene
Hybrid - offspring of two different true-breeding varieties
Monohybrid cross - mating of two organisms that differ in only one
character
Phenotype - observable traits of an organism
Recessive - descriptive of an allele in a heterozygous individual
that does not appear to affect a trait
Testcross - mating of an individual of unknown genotype but
dominant phenotype with a homozygous recessive individual
Introduction
The cutting edge of science
is genetics. From a few
drops of blood scientist can
test for all sorts of diseases
and treat many of them. But
the study of genetics is not as new as you
would assume. In fact, the study of
genetics was started in the 19th century (1800s) by a
monk named Gregor Mendel.
Mendel’s work


Mendel was not a famous scientist.
Instead he was a monk and a lowly
science teacher who was naturally
curious. He became the father of
genetics by accident.
Mendel started experimenting with
pea plants for the fun of it. He did
not set out to found a new field of
study.
Mendel’s work

Mendel studied pea plants for two
reasons



He could control the plant’s pollination
Many of the plant’s traits had two
possibilities and were very easy to see.
He worked for seven years and
performed thousands of
experiments before he came up
with his laws of segregation.
Mendel’s work



Mendel’s first experiments used two true
breeding plants that differed by only one
trait. This is called a monohybrid cross.
He observed that one of the traits seen in
the true breeding parents disappeared in
the first generation but reappeared in the
second generation in a predictable ratio.
From these experiments Mendel made 4
hypotheses.
Mendel’s hypotheses


There are multiple forms of genes
called alleles.
An organism has two alleles for
each gene. They receive 1 allele
from each parent. If the two alleles
are the same, the organism is
Homozygous. If the two alleles are
different, the organism is
Heterozygous
Mendel’s hypotheses


There are multiple forms of genes
called alleles.
An organism has two alleles for
each gene. They receive 1 allele
from each parent. If the two alleles
are the same, the organism is
Homozygous. If the two alleles are
different, the organism is
Heterozygous
Pea characteristics

Mendel studied 7 characteristics of
the pea plant. For each one he
found a dominant trait and a
recessive trait as his third
hypothesis says.
Lesson Review

Congratulations
You have finished
the lesson.