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Class
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Skills Worksheet
Directed Reading
Section: Studying Heredity
Complete each statement by writing the correct term or phrase in the space provided.
1. In a test cross to determine if an individual with a dominant phenotype is
heterozygous or homozygous for the trait, you always cross the individual
with a homozygous
individual.
2. If the offspring of a test cross all have the dominant trait, then the genotype
of the individual being tested is
.
3. If some of the offspring of a test cross have the recessive trait, then the
genotype of the individual being tested is
.
4. The probability that a gamete from a plant with a Tt genotype will carry a
t allele is
.
5. The probability of homozygous recessive offspring resulting from a cross
between two homozygous dominant individuals is
.
6. The probability of heterozygous offspring resulting from a cross between two
heterozygous individuals is
.
Read each question, and write your answer in the space provided.
7. When studying a pedigree, how do scientists determine if a trait is sex-linked
or autosomal?
8. When studying a pedigree, how do scientists determine if a trait is dominant
or recessive?
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Holt Biology
5
Mendel and Heredity
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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
1.
2.
3.
4.
5.
11.
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.
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