Download (pages 110–115) Mendel`s Experiments (pages 111–112)

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Date
Genetics: The Science of Heredity
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Mendel’s Work
Class
Adapted Reading and Study
(pages 110–115)
Mendel’s Experiments
(pages 111–112)
Key Concept: In all of Mendel’s crosses, only one form
of the trait appeared in the F1 generation. However,
in the F2 generation, the “lost” form of the trait
reappeared in about one fourth of the plants.
• In the mid 1800s, Gregor Mendel used garden peas to
study how traits were passed from parents to offspring.
A trait is a characteristic, such as seed color.
• The passing of traits from parents to offspring is called
heredity. The study of heredity is called genetics.
• Mendel started his experiments with purebred pea
plants. A purebred always produces offspring that have
the same trait.
• In one experiment, Mendel crossed purebred tall plants
with purebred short plants. When Mendel crossed the
plants, he took pollen from a flower on the tall plant and
used it to pollinate a flower on a short plant. He
collected the seeds that formed and grew them. All the
offspring plants were tall. The trait for shortness seemed
to disappear.
• Mendel allowed the offspring plants to pollinate
themselves. When he planted the seeds, he saw some
short plants. About one fourth of the plants were short.
Answer the following questions. Use your textbook and the
ideas above.
.
2. The study of heredity is called
.
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Genetics: The Science
of Heredity
1. The passing of traits from parents to offspring is called
Name
Date
Genetics: The Science of Heredity
■
Class
Adapted Reading and Study
3. Circle the letter that explains why Mendel used
purebred plants.
a. Purebred plants produce many offspring.
b. Purebred plants produce offspring with
different traits.
c. Purebred plants produce offspring with the
same trait.
4. Fill in the flowchart about Mendel’s first experiment
with pea plants.
Mendel’s Experiment
Mendel crossed purebred tall plants with purebred
a.
plants.
The offspring were all b.
.
Mendel allowed the offspring to pollinate themselves.
This second group of offspring were both
c.
.
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54
Name
Date
Genetics: The Science of Heredity
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Class
Adapted Reading and Study
Dominant and Recessive Alleles
(pages 113–115)
Key Concept: An organism’s traits are controlled by
the alleles it inherits from its parents. Some alleles are
dominant, while other alleles are recessive.
• Mendel concluded that separate factors control how
traits are inherited. These factors are in pairs, with one
factor from the mother and one from the father.
• Today, scientists call the factors that control traits
genes. The different forms of a gene are called alleles
(uh LEELZ). For example, the gene for stem height in pea
plants has two alleles—one for tall stems and one for
short stems.
• A dominant allele always shows up in an organism,
even when the other allele is present. A recessive allele
is hidden whenever the dominant allele is present.
• In Mendel’s crosses, the purebred parent plants had two
alleles for tall stems. The purebred short plants had two
alleles for short stems. The offspring plants had
one allele for tall stems from the tall parent and one
allele for short stems from the short parent.
• The offspring plants from Mendel’s crosses are called
hybrids. A hybrid (HY brid) has two different alleles for a
trait. All the offspring plants were tall because the
dominant allele for tall stems covers up the recessive
allele for short stems.
• Geneticists use letters to represent alleles. A dominant
allele has a capital letter. The allele for tall plants is T. A
recessive allele has the lowercase letter. The allele for
short plants is t. A purebred tall plant is TT. A purebred
short plant is tt. A hybrid tall plant is Tt.
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55
Name
Date
Genetics: The Science of Heredity
■
Class
Adapted Reading and Study
Answer the following questions. Use your textbook and the
ideas on page 55.
5. Is the following sentence true or false? Factors that
control traits are called genes.
6. Fill in the table about alleles of genes.
Alleles of Genes
Type of Allele
Description
Represented by
Dominant
always shows
up when present
a.
Recessive
b.
lowercase letter, t
7. Look at the two pea plants in the picture. Circle the
letter of the plant that could be a hybrid.
a.
b.
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56