Gregor Mendel’s Experiments, Theories, and Findings

Gregor Mendel’s Experiments, Theories, and Findings
1. Mendel observed that pea plants had traits, such as color, that were either “one or the other,” never
something in between. While DNA had yet to be discovered, he knew there were “factors involved in the
observable traits of his pea plants. Let’s imagine that we are studying only one trait, that of green- or
yellow-colored seeds. Mendel bred his peas until they either produced seeds of one color or the other.
These purebred plants he called the p generation (“p” for parental generation). He then cross bred green
plants with yellow ones and discovered that all the offspring were yellow-colored. Mendel called the
offspring of the purebred plants the F1 generation.
In your own words, explain why all the offspring in the F1 generation were yellow instead of half being
yellow and half green, or some other mix of the colors. Be sure to use the genetic term for these color-
determining “factors” and remember Mendel coined the terms dominant and recessive.
Your response should be at least 75 words in length. (Type your response in the box below.) (20 pts.)

Solving Punnett Squares
Reginald Punnett was a British geneticist who developed the Punnett square to explain how the
chromosomes of parents cross and produce offspring. In order to solve genetics problems using a
Punnett square, it is necessary to a) understand the associated vocabulary and b) understand some of
the rules for solving the problems.
 Before you continue with the problems below, review the meaning of the terms allele, dominant,
recessive, homozygous, heterozygous, genotype and phenotype.
 You should also review the Punnett Square Basics video linked in the unit lesson.
In this first problem (question #3), the key and genotype of the parents will be done for you as an
example. For problems #4 and #5, you will fill in those details based on the information in the question.
Remember, when asked for the genotypic ratio, it may be expressed as 25%(GG):50%(Gg):25%(gg), for
example. Or, you may write it more succinctly as 1GG:2Gg:1gg. Either way will be correct.

The phenotypic ratio will use descriptive terms, for example, 3(Green):1(clear), 2(Green):2(clear), or
whatever it may be depending on the results of your cross.
Punnett Square Problems
2. In corn plants, the allele for green kernels (G) is dominant over clear kernels (g). Cross a homozygous
dominant plant with a homozygous recessive plant.
a.) Fill in the Punnett square below and give the ratios for each question beneath the Punnett
Square. (2 pts.)

Key: G = green kernels, g = clear kernels
Genotype of parents: _GG_ x _gg_
Parent #1

Parent #2

b.) What is the genotypic ratio of the offspring in Question 3? (3 pts.)

c.) What is the phenotypic ratio of the offspring in Question 3? (3 pts.)

3. a.) Yellow seeds are dominant over green seeds in pea plants. Cross a heterozygous (yellow seeded)
plant with a green seeded plant. (3 pts.)
Key: __________
Genotype of parents: __________ x __________

Parent #1

Parent #2

b.) What is the genotypic ratio of the offspring in Question 4? (3 pts.)

c.) What is the phenotypic ratio of the offspring in Question 4? (3 pts.)

4. a.) Now cross two of the heterozygous F1 offspring from question #4. (3 pts.)

Parent #1

Parent #2

b.) What is the genotypic ratio of the offspring in Question 5? (3 pts.)

c.) What is the phenotypic ratio of the offspring in Question 5? (3 pts.)

5. Consider the resulting ratio of crossing the two heterozygous pea plants in question #5. We will use
this ratio in a short activity exploring probability. Keep in mind that crossing two individuals that are
heterozygous for a certain trait is similar to flipping two coins. Each coin has two sides (we might think of
each side as an “allele”) and the chances of flipping heads/heads, heads/tails or tails/tails should be
similar to the ratio we see when crossing two heterozygotes.
For this simple activity, you will need two coins (pennies, nickels, dimes, quarters, or a mix of any of
those). Alternatively, you may google a coin-flipper simulator that will allow you to flip two coins at once.
You will also need a piece of scratch paper and a pen or pencil or a blank electronic document.
Directions: Flip the two coins simultaneously at least 50 times. For each flip of the pair of coins, you will
record the results on a piece of scratch paper. You might set up a table like the one below to record your
results. Once you have flipped the coins at least 50 times, enter the number of heads/heads, heads/tails
and tails/tails in Table 1 below.
Now determine the ratio for your results. You will do this by dividing the number for each result by the
total number of flips, and then multiply by 100.
(Example: If the number of heads/heads is 9 then 9/50 = .18, .18×100 = 18%), Repeat this mathematical
procedure for heads/tails and tails/tails); be sure to include your math in the table!

a.) Table 1 (8 pts.)

Heads/heads (hh)

Head/tails (ht)

Tails/tails (tt)
Ratio (hh:ht:tt)

b.) Compare the resulting ratio from the question #5 cross of two heterozygous parents to the ratio from
the coin flipping exercise. Are there similarities? If so, what are they? Enter answer in the box below. (3
pts.)

c.) What might be done to make the ratio from the coin flipping exercise become more similar to the ratio
from question #5? (Hint: Consider that more data equals better accuracy.) Enter answer in the box below.
(3 pts.)

Cancer Risk Factors
6. This question deals with cancer and risk factors. Begin by going to the website http://www.cancer.org/
Click “Cancer A-Z” in the upper left corner. The page that comes up will provide links to information on
breast cancer, colon and rectal cancer, lung cancer, prostate cancer, and skin cancer. Review the
information for each these cancers.
Next, write an essay that discusses your own risk factors for each type of cancer and steps you might
take to decrease those risk factors. Be sure to address all five types of cancer.
You do not have to disclose any actual personal information if you do not wish to do so. You may create a
fictional character and discuss his or her risk factors instead. Be sure to address all five types of cancer.
Your response must be at least 300 words in length. (Type your response below) (40 pts.)