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Genetics: The Science of Heredity Guided Reading and Study
Mendel's WorkThis section describes how Gregor Mendel identified the method by which
characteristics are passed from parents to their offspring.
Use Target Reading Skills
As you read, complete the outline about Mendel's work. use the red headingsfor the
main idea and the blue headings for the supporting ideas.
l. Mendel's experiments
A. crossing pea plantsB.
c.D.
B.
c.
D.
IntroductionO 1. Gregor Mendel experimented with hundreds of pea plants to
understand the process of
Match the term with its definition.
Term
2. heredity
3. genetics
4. traits
Mendel's Experiments
Definition
a. The scientific study of heredity
b. Physical characteristics
c. The passing of traits from parentsto offspring
5. In a flower, the female sex cells, or eggs, are produced by the
Pollen, which contains the male sex cells, is
produced by the
6. What are purebred organisms?
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Genetics: The Science of Heredity • Guided Reading and Study
Mendel's Work (continued)
7. Complete the flowchart below, which summarizes Mendel's first
experiment with pea plants.
Mendel's Experiment
Purebred tall plants are crossed with purebred
Fl offspring are all
Fl offspring are allowed to self-pollinate.
plants.
F2 offspring are and
8. Circle the letter of other traits in garden peas that Mendel studied.
C)
Oa. seed size, seed shape, seed color
b. seed color, pod color, flower shape
c. flower size, pod shape, seed coat color
d. pod color, seed shape, flower position
9. Two forms of the trait of seed shape in pea plants are
and
Dominant and Recessive Alleles
10. Circle the letter of each sentence that is true about alleles.
a. Recessive alleles are never present when dominant alleles are present.
b. Alleles are different forms of a gene.
c. A trait controlled by a dominant allele always shows up in the organism when
the allele is present.
d. Recessive alleles hide dominant alleles.
11. Is the following sentence true or false? Only pea plants that have two recessive
alleles for short stems will be short.
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Genetics: The Science of Heredity • Guided Reading and Study
Match the pea plant with its combination of alleles.
Pea Plant
12. purebred short
13. purebred tall
14. hybrid tall
Combination of Alleles
a.
b.
c.
Two alleles for tall stems
One allele for tall stems and one allele
for short stems
Two alleles for short stems
15. A dominant allele is represented by a(n)
letter.
16. A recessive allele is represented by a(n)
letter.
17. How might a geneticist write the alleles to show that a tall pea plant has
one allele for tall stems and one allele for short stems?
18. Is the following sentence true or false? Some scientists during Mendel's
time thought Mendel should be called the Father of Genetics.
O
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Name Date Class
Genetics: The Science of Heredity • Guided Reading and Study
Probability and HeredityThis section explains what probability is and how the laws ofprobability can be used
in the study ofgenetics.
Use Target Reading Skills
After you read the section, reread the paragraphs that contain definitions of Key
Terms. use all the information you have learned to write a definition of each Key
Term in your own words.
Principles of Probability
1. A number that describes how likely it is that an event will occur is called
2. Circle the letter of each answer that equals the probability that a tossed
coin will land heads up.
a. 1 in 2
b. 1 /2c. 50 percent
d. 20 percent
3. Is the following sentence true or false? When you toss a coin 20 times,
o
you will always get 10 heads and 10 tails.
4. If you toss a coin five times and it lands heads up each time, can you
expect the coin to land heads up on the sixth toss? Explain.
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Genetics: The Science of Heredity Guided Reading and Study
Probability and Heredity (contin ued)
Probability and Genetics
5. When Mendel crossed two hybrid plants for stem height (Tt), what
results did he always get?
6. Mendel realized that the principles of probability could be used to
the results of genetic crosses.
7. A chart that shows all the possible combinations of alleles that can result
from a genetic cross is called a(n)
8. Write in the alleles of the parents and the possible allele combinations of
the offspring in the Punnett square below. (Note that both parents are
tall. Three of the offspring are tall and one is short.)
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Genetics: The Science of Heredity Guided Reading and Study
Phenotypes and Genotypes
Match the term with its definition.
Term Definition
9. phenotype a.
10. genotypeb.
11. homozygous
12. heterozygousc.
d.
13. Mendel used the termheterozygous pea plants.
Codominance
Describes an organism with two
identical alleles for a trait
An organism's physical appearance,
or visible traits
An organism's genetic makeup, or
allele combinations
Describes an organism that has two
different alleles for a trait
to describe
14. Is the following sentence true or false? In codominance, the alleles are
neither dominant nor recessive.
15. In cattle, red hair and white hair are codominant. Cattle with both white
hair and red hair are
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Genetics: The Science of Heredity • Guided Reading and Study
The Cell and InheritanceThis section describes how one set of chromosomes from each parent is passed on to
the offspring.
Use Target Reading Skills
As you read, identify the evidence that supports the hypothesis that genes are found
on chromosomes. Write the evidence in the graphic organizer below.
Evidence
Grasshoppers: 24 chromosomesHypothesis in body cells, 12 in sex cells
Chromosomes are importantin inheritance.
Chromosomes and Inheritance
1. Circle the letter of each sentence that is true about what Sutton observed
about chromosome number.
a. Grasshopper sex cells have half the number of chromosomes as body cells.
b. Grasshopper body cells have half the number of chromosomes as sex cells.
c. Grasshopper body cells and sex cells have the same number of chromosomes.
d. When grasshopper sex cells join, the fertilized egg has the same number of
chromosomes as the body cells of the parents.
2. What is the chromosome theory of inheritance?
Meiosis
3. What is meiosis?
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Name Da te Class
Genetics: The Science of Heredity • Guided Reading and Study
The Cell and Inheritance (continued)
4. Complete the cycle diagram, which describes the events that occur
during meiosis.
Parent cell has four chromosomes
arranged in pairs.
Sex cells combine to produce offspring.
Each offspring has
chromosomes, one pair from each parent.
Chromosome pairs and are
distributed to sex cells. Each sex cell has
chromosomes.
5. A Punnett square is a shorthand way to show the events that occur
during
6. Is the following sentence true or false? During meiosis, the two alleles
for each gene stay together.
7. If the male parent cell is heterozygous for a trait, Tt, what alleles could
the sperm cells possibly have?
A Lineup of Genes
8. How many pairs of chromosomes do human body cells contain?
9. How are the genes lined up in a pair of chromosomes?
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Genetics: The Science of Heredity • Guided Reading and Study
8. List the two kinds of RNA and describe their jobs.
a.
b.
9. Circle the letter of the first step in protein synthesis.
a. Transfer RNA carries amino acids to the ribosome.
b. The ribosome releases the completed protein chain.
c. Messenger RNA enters the cytoplasm and attaches to a ribosome.
d. DNA "unzips" to direct the production of a strand of messenger RNA.
10. Circle the letter of the last step in protein synthesis.
a. Transfer RNA carries amino acids to the ribosome.
b. The protein chain grows longer as each transfer RNA molecule
adds an amino acid.
c. Messenger RNA enters the cytoplasm and attaches to a ribosome.
d. DNA "unzips" to direct the production of a strand of messenger RNA.
Mutations
11. What is a mutation?
12. How can mutations affect protein synthesis in cells?
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Genetics: The Science of Heredity • Guided Reading and Study
OThe DNA Connection (continued)
13. Circle the letter of each sentence that is true about mutations.
a. Cells with mutations will always make normal proteins.
b. Some mutations occur when one nitrogen base is substituted for another.
c. Some mutations occur when chromosomes don't separate correctly during
meiosis.
d. Mutations that occur in a body cell can be passed on to an offspring.
14. Mutations can be a source of genetic
15. Is the following sentence true or false? All mutations are harmful.
16. Mutations that are improve an organism's
chances for survival and reproduction.
17. Whether a mutation is harmful or helpful depends partly on an
organism's
O
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