Mendel’s
Experiments
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
Use your observations to answer the following questions.
2.
Did both of the parents look identical? ______ 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.
3.
Did all of the F1 offspring look identical? ______ If not, tell how they are different.
______________________________________________________________________
4.
Compare the appearance of the offspring to their parents. Did the offspring look
identical to 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.
5.
Which characteristic was represented in your envelope? _________________________
6.
Which trait was dominant? _______________________
7.
Which trait was recessive? _______________________
Mendel next wondered what would happen if the F1 generation became parents of new offspring.
MENDEL’S 2ND EXPERIMENT
8.
Observe the parent plant. Did it show the dominant or recessive trait?
_______________
Offspring of the F1 generation parent are called the F2 generation (or second generation).
9.
Did all of the F2 offspring look alike? ______ If not, tell how they are different. _______
______________________________________________________________________
10.
Compare the appearance of the F2 offspring to their F1 parent. Do all of the offspring
look like the parent? _______ If not, explain what you observe. __________________
______________________________________________________________________
11.
Organize your observations in the following table.
Characteristics
Plant Height
Flower Color
Pea Color
Pod Shape
Parent
F1
F2
12.
What is the pattern in the F1 generation? _____________________________________
13.
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.
14.
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? _________________
15.
If you inherit two dominant genes, which trait will show – dominant or recessive?
___________________________
What color would your eyes be? _________________
16.
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.
The first one has been done for you:
705 purple
224 white
=
3.15 purple
1 white
=
3 purple to 1 white = 3:1
(rounded)
Do your calculations and fill in the Ratio column.
3:1
16. What pattern do you see in
the ratios for the F2
offspring?___________________
___________________________
________________________
________________________
________________________
________________________
________________________
________________________
________
Create a graph to represent the data from Table 1 Mendel’s Results.