Mendel’s
Experiments
Name _____________________________
Science-_____ Date _________________
WHY DO I NEED TO KNOW THIS?
Genetics is a branch of biology that has to do with studying the inheritance patterns of specific
traits and is one of the most rapidly growing areas of science today. It is important for you to
have a basic knowledge of this science for many reasons. Genetics is used today to create new
medicines, improve treatments for diseases, develop new energy sources, and grow better crops
among other things. Forensic scientists also use knowledge of genetics for DNA profiling which
is used to link criminals to their crimes.
GREGOR MENDEL
Gregor Mendel is sometimes called the “Father of Genetics” because his experiments with pea
plants helped us to understand how traits are inherited. Let’s begin by learning who he was.
1.
Read the section titled “Who was Gregor Mendel?” on p. 56 and answer these questions.
When was Gregor Mendel born? _____________ Where? _________________________
Where did he learn about flowers and fruit trees? _______________________
When he was 21 years old, what did he do? ________________________________
What did Mendel go to school to study? ____________________________
What did Mendel discover? ____________________________________________
Where did he discover this? ___________________________________
Even though Mendel had difficulties in school, his curiosity led him to great discoveries. Using
scientific methods, he studied many different characteristics of pea plants (including flower color
and plant height). Let’s look at Mendel’s experiments to see what he discovered.
MENDEL’S 1ST EXPERIMENT
Put the green paper with the “Mendel’s 1st Experiment” side facing up. Open the envelope
labeled PARENTS and place the two sample plant parents in the parent space. Follow your
teacher's directions and draw both parent plants in the appropriate space. Make 3 observations of
the parent plants. HINT: look carefully at the details.
2. Do both of the parents look alike? ______ If not, tell how they are different. _____________
___________________________________________________________________________
Mendel “crossed” (cross-pollinated) these two plant parents and produced offspring. These
offspring are called the F1 generation. (F1 means the first generation after the parents.) Open the
envelope labeled F1 GENERATION and place the sample offspring in the F1 space. Follow
your teacher's directions and draw all of the F1 plants in the appropriate space. Make 4
observations of the F1 plants. HINT: again look carefully at the details.
3. Do all of the F1 offspring look alike? ______ If not, tell how they are different. __________
___________________________________________________________________________
4. Compare the appearance of the offspring to their parents. Do the offspring look like both of
the parents? _______ If not, explain what you observe. ____________________________
__________________________________________________________________________
Mendel’s first experiment shows only one parent trait appeared in the F1 generation of offspring.
The other parent trait disappeared. He called the trait that showed up dominant, and the trait
that did NOT show up he called recessive. (The word recessive means “to recede or hide.”) It
was a good word to use since the recessive trait seems to recede or hide in the F1 offspring.
Observe your sample plants.
5. Which trait is dominant? _______________________
6. Which trait is recessive? _______________________
Put the Parents and F1 generation back in the correct envelopes.
Mendel next wondered what would happen if the F1 generation became parents of new
offspring. Let’s see what happened.
MENDEL’S 2ND EXPERIMENT
Turn over the green paper to the side for “Mendel’s 2nd Experiment.” The F1 plants have
matured and will now become the parents. Remember, their genes are identical—one dominant,
and one recessive. Take out two of the F1 generation plants and put them in the F1 space.
7. Observe the parent plants. Do they show the dominant or recessive trait? _______________
Offspring of the F1 generation parent are called the F2 generation (or second generation after the
parents). Open the envelope labeled F2 GENERATION and place the sample offspring in the
F2 space. Follow your teacher's directions and draw all of the F2 plants in the appropriate space.
Make 5 observations of the F2 plants. HINT: again look carefully at all of the details.
8. Do all of the F2 offspring look alike? ______ If not, tell how they are different. __________
___________________________________________________________________________
9. Compare the appearance of the F2 offspring to their F1 parents. Do all of the offspring look
like the parents? _______ If not, explain what you observe. __________________________
__________________________________________________________________________
Put the F1 and F2 generations back in the correct envelopes.
THE STORY SO FAR… (During our class discussion, you will complete this chart.)
10.
What is the pattern in the F1 generation? ______________________________________
11.
What is the pattern in the F2 generation? ______________________________________
Mendel thought that there must be something in each plant that controlled its traits. He called
these things “factors” but we now call them genes. We also now know that each characteristic
(like flower color) is controlled by two genes—one gene is inherited from each parent.
The F1 plants have 1 dominant gene and 1 recessive gene, but only show the dominant trait.
That’s because the dominant gene masks (covers up) the recessive gene. When the F1 plants
became parents they were able to have some offspring that showed the recessive trait. How is
this possible?
If the offspring receive 1 recessive gene from one parent and 1 recessive gene from the other
parent, they have 2 recessive genes. Then, there is no dominant gene to mask the recessive gene.
You will see the recessive trait in the offspring.
We can apply what Mendel learned to people’s characteristics, too. Let’s look at eye color as an
example. Dark eye color is a dominant trait and light eye color is a recessive trait.
12. If you inherit one dominant gene from your mom and one recessive gene from your dad,
then which trait will show – the dominant trait or the recessive trait? ___________________
What color would your eyes be? _________________
13. If you inherit two dominant genes, which trait will show – dominant or recessive?
___________________________
What color would your eyes be? _________________
14. If you inherit two recessive genes, which trait will show – dominant or recessive?
__________________________
What color would your eyes be? _________________
RATIOS
The F2 offspring showed two different traits for each characteristic. Many offspring showed the
dominant trait. A few offspring showed the recessive trait. Can we be more specific than
“many” and “a few”? Yes, we can. It is very common to use a ratio to express the number of
offspring showing the dominant trait compared to the recessive trait. On the next page you are
going to calculate these ratios from the actual data collected by Gregor Mendel at his monastery.
Here is how to calculate the ratio of dominant to recessive traits for each characteristic:
A. Use the number of dominant traits and recessive traits to write an improper fraction.
B. Divide both the numerator and denominator by the smaller number.
C. Round off the numerator to the nearest whole number and write as a ratio.
The first one has been done for you:
705 purple
224 white
:
224
224
=
3.15 purple
1 white
=
3 purple to 1 white = 3:1
(rounded)
Do your calculations and fill in the Ratio column.
Mendel’s Results for F2 Offspring
3:1
16. What pattern do you see in the ratios for the F2 offspring? ___________________________
______________________________________________________________________________
Name _______________________________________ Date __________________ per. ______
Quick Question - A child is born to 2 parents. The mother has brown eyes – a dominant trait.
The father has brown eyes also. The child has blue eyes – a recessive trait. How is this
possible? Write an explanation below. Use the words “dominant”, “recessive”, and “gene(s)” in
your summary.
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Name _______________________________________ Date __________________ per. ______
Quick Question - A child is born to 2 parents. The mother has brown eyes – a dominant trait.
The father has brown eyes also. The child has blue eyes – a recessive trait. How is this
possible? Write an explanation below. Use the words “dominant”, “recessive”, and “gene(s)” in
your summary.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
_____________________________________________________________________________
Name _______________________________________ Date __________________ per. ______
Quick Question - A child is born to 2 parents. The mother has brown eyes – a dominant trait.
The father has brown eyes also. The child has blue eyes – a recessive trait. How is this
possible? Write an explanation below. Use the words “dominant”, “recessive”, and “gene(s)” in
your summary.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
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