Name:___________________________
Hour:_____
Mendelian Genetics
Read the passage below to help answer the following questions.
Mendel’s initial experiments were monohybrid crosses. A monohybrid cross is a cross that involves one pair of
contrasting traits. For example, crossing a plant with purple flowers and a plant with white flowers is a monohybrid
cross. Mendel carried out his experiments in three steps.
Step 1: Mendel allowed each variety of garden pea plants to self-pollinate for several generations. This method
ensured that each variety was true-breeding for a particular trait; that is, all the offspring would display one form of a
particular trait. For example, a true-breeding purple-flowering plant should produce only plants with purple flowers in
subsequent generations. (See first two boxes of Figure 1)
These true-breeding plants served as the parental generation in Mendal’s
experiments. The parental generation, or P generation, are the first two
individuals that are crossed in a breeding experiment.
Step 2: Mendel then cross-pollinated two P generation plants that had
contrasting forms of a trait such as purple and white flowers. Mendel called
the offspring of the P generation the first filial (relating to) generation or F1
generation. He then examined each F1 plant and recorded the number of F1
plants expressing each trait.
Figure 1
Step 3: Finally, Mendel allowed the F1 generation to self-pollinate. He called the offspring of the F1 generation plants
the second filial generation, or the F2 generation. Again, each F2 plant was characterized and counted.
1. The prefix mono- means “one.” How does this apply to the key term monohybrid cross?
2. Describe the offspring of a true-breeding white-flowering plant.
3. What is the P generation?
4. What does the term F1 generation refer to?
5. Analyze figure 1 and then summarize Mendel’s experiment and his findings.
6. During the course of his experiment, Mendel studied traits for three generations. Compare Mendel’s P, F1, and
F2 generations to generations in your family. (Hint: Assume your grandparents are the P generation. In Mendel’s
terms what generation does that make your parents?)
Read the passage below to help answer the following questions.
Geneticists have developed specific terms and ways of representing an individual’s genetic makeup. Letters are often
used to represent alleles. Dominant alleles will mask (hide) the presence of another allele for the same characteristic
and is indicated by writing the first letter of the trait as a capital letter. Recessive alleles can be masked (hidden) by the
presence of a dominant allele and is represented by a letter written in
a lowercase.
If two alleles of a particular gene present in an individual are the same
(TT or tt), the individual is said to be homozygous for that trait. If the
alleles of a particular gene present in an individual are different (Tt),
the individual is heterozygous for that trait.
Every organism has a genetic makeup as well as a set of observable
characteristics. These observable characteristics are called
phenotypes. Peas have distinctive traits that are inherited in
predictable ways. Figure 3 shows all seven traits that Mendel studied,
each having two phenotypes. For example, all purple plants have the
same phenotype. They do not however have the same genotype,
or genetic makeup. In analyzing figure 2 you will find three
different genotypes among the F2 plants: PP, Pp, and pp. The
genotype of an organism is inherited, and the phenotype is
largely determined by the genotype. Two organisms may share
the same phenotype but have different genotypes.
Figure 2
Figure 3
1. How are the dominant alleles represented?
2. How are the recessive alleles represented?
3. A particular plant is said to be homozygous for seed color. What does this mean?
4. Another plant is said to be heterozygous for flower color. What does this mean?
5. The allele for yellow peas is dominant to the allele for green peas. How would you represent the alleles of a
plant that is heterozygous for seed color?
6. The allele for purple flowers is dominant to the allele for white flowers. How would you represent the alleles of
a plant that is homozygous recessive for flower color?
7. How would you represent the alleles of a plant that is heterozygous for flower color?
8. A plant with YY alleles for seed color is classified as _________________________.
9. Explain how it is possible for two organisms to share the same phenotype but have different genotypes.
10. Other than flower color, list three other traits that Mendel studied? What were possible phenotypes of each?
11. Why does a genotype contain two letters?
12. The genotype of a true-breeding purple flowered pea plant is PP and the genotype of a true-breeding white
flowered plant is pp.
a. What do you think the genotype of the F1 generation plants are? Explain.
b. What do you think the genotypes of the F2 generation are? Explain.
Use Figure 4 to help you answer the following questions.
Figure 4
13. Write the possible genotypes for the following phenotypes:
a. yellow seeded plant ________
b. wrinkled seeded plant ________
c. inflated pod ________
d. smooth seeded plant _______
14. Write the phenotype for the given genotypes:
a. Tt _____________________
b. DD ____________________
c. aa _____________________
d. Gg _____________________