Download Mendel`s Experiments

Mendel’s
Experiments
Name ___________________________________
Period ___________________________________
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 from Friday’s envelops (Parents, F1, and F2) to answer the following questions.
2.
Did both of the parents look identical? ______ If not, tell how they are different.
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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.
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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.
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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, so he selfpollinated one of the F1 generation plants. This plant became the parent plant of the F2 generation plants.
MENDEL’S 2ND EXPERIMENT
8.
Observe the parent plant from the F1 generation. Did it show the dominant or recessive trait?
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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. ___________________
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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. _________________________________________
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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.
11.
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? ________________________________________________________
12.
If you inherit two dominant genes, which trait will show – dominant or recessive?
__________________________________________________________________________________
What color would your eyes be? ________________________________________________________
13.
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.
14. What pattern do you see in the ratios for the
F2 offspring?
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3:1
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Create a graph to represent the data from Table 1 Mendel’s Results.