Download HRW BIO CRF Ch08_p01-66

Back
Print
Name
Class
Date
Skills Worksheet
Active Reading
Section: The Origins of Genetics
Read the passage below. Then answer the questions that follow.
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 only one form of a particular trait. For
example, a true-breeding purple-flowering plant should produce
only plants with purple flowers in subsequent generations.
These true-breeding plants served as the parental generation
in Mendel’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 generation, or F1 generation. He then examined each F1
plant and recorded the number of F1 plants expressing each trait.
Step 3: Finally, Mendel allowed the F1 generation to selfpollinate. He called the offspring of the F1 generation plants the
second filial generation, or F2 generation. Again, each F2 plant
was characterized and counted.
SKILL: READING EFFECTIVELY
Read each question, and write your answer in the space provided.
1. The prefix mono- means “one.” How does this apply to the key term
monohybrid cross?
2. What information does the third sentence tell the reader?
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Biology
9
Mendel and Heredity
Back
Print
Name
Class
Date
Active Reading continued
3. Describe the offspring of a true-breeding white-flowering plant.
4. What is the P generation?
5. What does the term F1 generation refer to?
SKILL: INTERPRETING GRAPHICS
The figure below shows three generations of plants. Insert the following labels in
the spaces provided: cross-pollination, F1, F2 , P, self-pollination.
6.
generation
7.
generation
9.
8.
generation
10.
In the space provided, write the letter of the phrase that best completes the
statement.
______11. During the course of his experiment, Mendel studied traits in
a. one generation of plants.
b. two generations of plants.
c. three generations of plants.
d. more than five generations of plants.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Biology
10
Mendel and Heredity
Back
Print
TEACHER RESOURCE PAGE
Answer Key
Directed Reading
have a parent with the trait. If a trait is
recessive, an individual with the trait
may have one, two, or no parents with
the trait.
SECTION: THE ORIGINS OF
GENETICS
1. Knight discovered that the purple-
2.
3.
4.
5.
6.
7.
SECTION: COMPLEX PATTERNS
OF HEREDITY
flowered offspring of a cross between
garden peas with purple flowers and
garden peas with white flowers produce some offspring with purple flowers and some with white flowers.
Mendel carefully counted the number
of each kind of offspring, analyzed the
data, and discovered that the numbers
formed simple ratios.
Garden peas have many traits with
two clearly different forms; it is easy
to control matings in garden peas; and
garden peas are small, mature quickly,
and produce numerous offspring.
monohybrid
P
F1
F2
1. A polygenic trait is a trait that is influ-
2.
3.
4.
5.
6.
SECTION: MENDEL’S THEORY
f
6. e
a
7. d
g
8. y
b
9. tall
c
10. short
The law of segregation states that the
two alleles for a trait segregate when
gametes are formed during meiosis.
12. The law of independent assortment
states that the pairs of alleles for different traits separate independently of
one another during meiosis.
1.
2.
3.
4.
5.
11.
enced by several genes. A trait determined by multiple alleles is controlled
by a gene that has three or more alleles.
Incomplete dominance occurs when
offspring display a form of a trait that
is intermediate between the forms of
the trait displayed by the parents.
Codominance occurs when two alleles
for a characteristic are expressed at
the same time.
proteins
cystic fibrosis
people with a family history of genetic
disorders
Gene therapy is a procedure that
attempts to replace defective genes by
inserting copies of healthy genes into
an individual.
Active Reading
SECTION: THE ORIGINS OF
GENETICS
1. A monohybrid cross involves only one
2.
3.
4.
SECTION: STUDYING HEREDITY
1. recessive
2. homozygous
3. heterozygous
1
4. 2
5.
6.
7.
8.
9.
10.
11.
5. 0
1
6. 2
7. If a trait is autosomal, it will appear
equally in both sexes.
8. If an autosomal trait is dominant,
every individual with the trait will
pair of contrasting traits.
It provides a specific example of a
monohybrid cross.
This plant would produce only plants
with white flowers.
The parental generation is the first
two individuals that are crossed in a
breeding experiment.
the first filial generation or first offspring of the parental generation
P
F1
F2
cross-pollination
self-pollination
c
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Biology
86
Mendel and Heredity