Name ______________________________ Class___________________Date__________________
Extending Mendelian Genetics
Study Guide A
Answer Key
SECTION 1. CHROMOSOMES AND
PHENOTYPE
SECTION 3. GENE LINKAGE AND
MAPPING
1. sex; autosomes
2. does not; can
3. Autosomal Recessive: DD, no disorder; Dd,
carrier; Dd, carrier; dd, disorder
Autosomal Dominant: DD, disorder; Dd,
disorder; Dd, disorder; dd, no disorder
4. sex chromosomes
5. XX, female; XX, female; XY, male;
XY, male
6. either X or Y; only X
7. male
8. row 1: males; row 2: females
9. offspring
10. females; “turned off”
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
SECTION 4. HUMAN GENETICS AND
PEDIGREES
1.
2.
3.
4.
5.
6.
7.
8.
b and d
c
autosomal
Males
genotypes
phenotype
d
XdXd
XdY
female carrier
must have XDXd, XDY; could have XDXD,
XDXd, XDY, XdY
must have XDXd, XdY; could have XDXd,
XdXd, XDY, XdY
must have XdXd, XDY; could have
XDXd, XdY
must have XdXd, XdY; could have XdXd,
XdY
9. karyotypes; genetic testing (genetic
screening)
10. chromosomes
11. picture
SECTION 2. COMPLEX PATTERNS
OF INHERITANCE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
together
quickly; easy
most common; much less
chromosome; independently; cross-over
Mendel: b and c; Punnett and Bateson: b and
e; Morgan: a, d, and f
closer; farther apart
meiosis
c
b
a and c
A–7–D–13–B–5–C
b, d, f
a, e
more than
b
d
a
c
genes; phenotypes
expression
environment
temperature; nutrition / health care
incomplete dominance
codominance
polygenic traits
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
i
Extending Mendelian Genetics
Name ______________________________ Class___________________Date__________________
Section 1: Chromosomes and Phenotype
Study Guide A
KEY CONCEPT
The chromosomes on which genes are located can affect the expression of traits.
VOCABULARY
carrier
sex-linked gene
X chromosome inactivation
MAIN IDEA: Two copies of each autosomal gene affect phenotype.
Fill in the blank or circle the word or phrase that best completes the sentence.
1. Sex chromosomes determine an organism’s _______________. All other
chromosomes, which do not directly affect an organism’s sex, are called
_______________.
2. A person who is a carrier differs from a person who has a genetic disorder. A
carrier does / does not show symptoms of a disorder but can / cannot pass the
disorder to offspring.
3. Complete the two Punnett squares below to compare autosomal recessive
disorders with autosomal dominant disorders.
Fill in the possible genotypes for offspring, and write in the phenotype
(no disorder, carrier, or disorder) for each.
Autosomal Recessive
D
Autosomal Dominant
d
D
D
D
d
d
d
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
1
Extending Mendelian Genetics
Section 1: Chromosomes and Phenotype
Name ______________________________ Class___________________Date__________________
Study Guide A continued
MAIN IDEA: Males and females can differ in sex-linked traits.
4. Sex-linked genes are located on the _____________________.
5. Fill in the Punnett square below to show the pattern of inheritance for sex
chromosomes. Write in the phenotype (male or female) for each.
Sex Chromosome Inheritance
X
X
X
Y
Circle the word or phrase that best completes the statement.
6. In humans, a gamete from a male determines the sex of the offspring, because
a male can pass on only X / only Y / either X or Y chromosomes. In contrast, a
female passes on only X / only Y / either X or Y chromosomes.
7. The genes on the Y chromosome are responsible for male / female
characteristics.
8. Place a check mark in the appropriate boxes to show how sex-linked genes are
expressed in the phenotypes of males and females.
Males
Females
Show phenotypes from all sex-linked genes.
Show phenotypes similarly to autosomal gene expression.
Vocabulary Check
Circle the word or phrase that best completes the statement.
9. The verb carry means “to transport.” This meaning is related to the term
carrier in genetics, because a carrier is a person who “transports” a
disease-causing allele to offspring / parents.
10. With X chromosome inactivation, which occurs in males / females, one of the
two X chromosomes in every cell is randomly “turned off” / “turned up.”
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
2
Extending Mendelian Genetics
Section 1: Chromosomes and Phenotype
Name ______________________________ Class___________________Date__________________
Section 2: Complex Patterns of Inheritance
Study Guide A
KEY CONCEPT
Phenotype is affected by many different factors.
VOCABULARY
incomplete dominance
codominance
polygenic trait
MAIN IDEA: Phenotype can depend on interactions of alleles.
1. Circle the letter of all of the following statements that are true about
incomplete dominance.
a. Both alleles are completely expressed.
b. Neither allele is completely dominant.
c. Neither allele is expressed.
d. One allele is not hidden in a heterozygote.
e. Heterozygous phenotype contains the separate products of both alleles.
f. Heterozygous phenotype is somewhere between the homozygous
phenotypes.
2. Circle the letter of all of the following statements that are true
about codominance.
a. Both alleles are completely expressed.
b. Neither allele is completely dominant.
c. Neither allele is expressed.
d. One allele is not hidden in a heterozygote.
e. Heterozygous phenotype contains the separate products of both alleles.
f. Heterozygous phenotype is somewhere between the homozygous
phenotypes.
Circle the word or phrase that best completes the statement.
3. With a multiple-allele trait, the gene has less than / only / more than two
alleles.
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Holt McDougal Biology
Study Guide A
3
Extending Mendelian Genetics
Section 2: Complex Patterns of Inheritance
Name ______________________________ Class___________________Date__________________
Study Guide A continued
Place the following statements into the appropriate boxes to indicate how
phenotypes appear in incomplete dominance and codominance and to provide
an example of each.
a. A third phenotype that has both of the homozygous parental phenotypes.
b. A third, distinct phenotype that has neither of the homozygous parental
phenotypes.
c. Blood type (one parent has blood type A, one parent has blood type B,
offspring has blood type AB).
d. The 4 o’clock plant (one parent has red flowers, one parent has white
flowers, offspring has pink flowers).
Interaction
Phenotype
Example
Incomplete dominance
4.
5.
Codominance
6.
7.
MAIN IDEA: Many genes may interact to produce one trait.
Fill in the blank with the word or phrase that best completes the sentence.
8. Polygenic traits are produced by two or more ______________ and show a
continuous range of ______________. One example is eye color.
9. Epistasis is the term for one gene affecting the ________________ of other
genes involved in a particular trait. One example is albinism.
MAIN IDEA: The environment interacts with genotype.
10. Genotype is not the only factor that affects phenotype. The _______________
can affect gene expression, which will influence phenotype.
11. Complete the following sentences, which give examples of how environment
and genotype can interact.
In sea turtles, sex determination depends on both genes and the
__________________ at which sea turtle eggs mature.
In humans, height is affected by both genes and factors such as
__________________.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
4
Extending Mendelian Genetics
Section 2: Complex Patterns of Inheritance
Name ______________________________ Class___________________Date__________________
Study Guide A continued
Vocabulary Check
Fill in the blank with the word or phrase that best completes the sentence.
12. The prefix in- means “not.” In genetics, the term _____________________
means that neither allele is dominant.
13. The prefix co- means “together.” In genetics, the term ___________________
means that both alleles are expressed together.
14. The prefix poly- means “many,” and the term genic means “related to genes.”
Traits that are produced by two or more genes are called
______________________.
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Holt McDougal Biology
Study Guide A
5
Extending Mendelian Genetics
Section 2: Complex Patterns of Inheritance
Name ______________________________ Class___________________Date__________________
Section 3: Gene Linkage and Mapping
Study Guide A
KEY CONCEPT
Genes can be mapped to specific locations on chromosomes.
VOCABULARY
linkage map
MAIN IDEA: Gene linkage was explained through fruit flies.
Fill in the blank or circle the word or phrase that best completes the statement.
1. Gene linkage describes genes that are on the same chromosome and tend to be
inherited separately / together.
2. Fruit flies were useful in Morgan’s research, because many generations of fruit
flies could be grown slowly / quickly, and fruit flies had traits that were easy /
difficult to observe.
3. A wild type differs from a mutant type. A wild type is the least common / most
common phenotype, and a mutant type is a much less / much more common
phenotype.
4. Morgan made several conclusions from his research on fruit flies:
Linked genes are on the same _________________.
Chromosomes, not genes, assort ________________ during meiosis.
Homologous genes can be exchanged through _________________ during
meiosis.
5. The sequence diagram on the following page shows how scientific work
progressed in the discovery of gene linkage.
Place the statements below into appropriate boxes in the diagram on the next
page. Some statements may go into more than one box.
a. Studied fruit flies.
b. Studied pea plants.
c. Suggested that genes assort independently of one another.
d. Suggested that chromosomes assort independently.
e. Suggested that some genes are linked.
f. Concluded that linked genes were on the same chromosome.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
6
Extending Mendelian Genetics
Section 3: Gene Linkage and Mapping
Name ______________________________ Class___________________Date__________________
Study Guide A continued
Mendel:
Punnett, Bateson:
Morgan:
MAIN IDEA: Linkage maps estimate distances between genes.
Circle the word or phrase that best completes the statement.
6. The distance between two genes is related to the chance that they are inherited
together. The closer / farther apart genes are, the more likely they will be
inherited together. The closer / farther apart they are, the more likely they are
to be separated.
7. The basis of Sturtevant’s research was the hypothesis that the frequency of
cross-overs during meiosis / mitosis is related to the distance between genes.
8. What is a linkage map?
a. A map of each gene’s phenotype relative to other genes.
b. A map of each gene’s shape relative to other genes.
c. A map of the relative locations of genes on a chromosome.
d. A map of the relative sizes of genes on a chromosome.
9. How are cross-over frequencies related to linkage maps?
a. The percentage of cross-overs is added to the map linkages.
b. The percentage of cross-overs is converted into map units.
c. The percentage of cross-overs is generated by map units.
d. The percentage of cross-overs is subtracted from the percentage of linkages.
10. What two things do linkage maps show about genes on a chromosome?
a. An estimate of physical distance between genes.
b. The actual physical distance between genes.
c. The relative locations of genes.
d. The relative sizes of genes.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
7
Extending Mendelian Genetics
Section 3: Gene Linkage and Mapping
Name ______________________________ Class___________________Date__________________
Study Guide A continued
11. Use the cross-over frequencies given below to draw a linkage map for the four
genes listed. Think about the relationship between cross-over frequency and
distance in linkage map units. Use Figure 3.3 to help you make the linkage
map. Put gene A on the far left of the map, then work through the distances
between the gene pairs.
Cross-over Frequencies:
A-B
20%
B-C
5%
A-C
25%
A-D
7%
D-B
13%
D-C
18%
Linkage Map
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
8
Extending Mendelian Genetics
Section 3: Gene Linkage and Mapping
Name ______________________________ Class___________________Date__________________
Section 4: Human Genetics and Pedigrees
Study Guide A
KEY CONCEPT
A combination of methods is used to study human genetics.
VOCABULARY
pedigree
karyotype
MAIN IDEA: Human genetics follows the patterns seen in other organisms.
1. Circle two ways in which genetic inheritance follows similar patterns in all
sexually reproducing organisms.
a. All chromosomes can be mapped on a single linkage map.
b. Chromosomes assort independently during meiosis.
c. Genes determine the same phenotypes.
d. Relationships among alleles are the same.
2. Single-gene traits are useful in studying human genetics because:
a. inheritance is always recessive.
b. inheritance is independent of the gene.
c. inheritance is straight-forward.
d. inheritance is exponential.
MAIN IDEA: Females can carry sex-linked genetic disorders.
Circle the word or phrase that best completes the statement.
3. Both males and females with a recessive disorder-causing allele can be
carriers of a(n) sex-linked / autosomal disorder and pass on the disorder to
their offspring.
4. Males / Females are not carriers of sex-linked genetic disorders, because they
cannot have a normal, dominant allele to mask the effect of a recessive,
disorder-causing allele.
MAIN IDEA: A pedigree is a chart for tracing genes in a family.
Fill in the blank with the word or phrase that best completes the sentence.
5. A pedigree is a chart that traces phenotypes and ____________ in a family.
6. In pedigree analysis, the _______________ is used to infer the genotype.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
9
Extending Mendelian Genetics
Section 4: Human Genetics and Pedigrees
Name ______________________________ Class___________________Date__________________
Study Guide A continued
7. A pedigree can tell you whether a gene is most likely on an autosome or on a
sex chromosome. The gene is most likely autosomal if:
a. only males show the phenotype.
b. all females and a few males show the phenotype.
c. all males and a few females show the phenotype.
d. approximately the same number of males and females show the phenotype.
8. Complete the chart to follow the logic necessary to fill out a pedigree for a
sex-linked gene. Use XD and Xd for the dominant and recessive X-linked
genes, respectively.
Tracing Sex-Linked Genes
Phenotype
Female, recessive phenotype
Male, recessive phenotype
must
have
must
have
must
have
must
have
Genotype
XD Xd
Parental
Phenotype
must
have
Female carrier,
normal male
must
have
could
have
Female carrier, male
must
with recessive
have
phenotype
could
have
Female with
recessive phenotype, must
have
normal male
could
have
Female with
recessive phenotype, must
male with recessive have
phenotype
could
have
could
have
Parental
Genotype
Offspring
Genotypes
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
10
Extending Mendelian Genetics
Section 4: Human Genetics and Pedigrees
Name ______________________________ Class___________________Date__________________
Study Guide A continued
MAIN IDEA: Several methods help map human chromosomes.
Fill in the blank with the word or phrase that best completes the sentence.
9. Two methods that are used to directly study human chromosomes are
______________________ and __________________________.
10. A karyotype can show any large-scale changes in ___________________.
Vocabulary Check
Fill in the blank with the word that best completes the sentence.
11. A karyotype is a ___________________ of all the chromosomes in a cell.
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide A
11
Extending Mendelian Genetics
Section 4: Human Genetics and Pedigrees