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SEC T I O N 1 2 - 1 R E VIEW
C HROMOSOMES AND I NHERITANCE
VOCABULARY REVIEW Distinguish between the terms in each of the following pairs
of terms.
1. sex chromosome, autosome
2. germ-cell mutation, somatic-cell mutation
3. translocation, nondisjunction
4. deletion, inversion
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5. substitution, frameshift mutation
MULTIPLE CHOICE Write the correct letter in the blank.
1. Genes that belong to the same linkage group tend to be
a. located on different chromosomes.
b. inherited together.
c. found only in males.
d. found only in somatic cells.
2. Two genes that are one map unit apart are separated by crossing-over
a. 1% of the time.
b. 20% of the time.
c. 50% of the time.
d. 100% of the time.
c. germ cells.
d. skin cells.
3. Mutations that can be inherited arise in
a. somatic cells.
b. body cells.
4. Which of the following sequences could result from an inversion of the sequence GAGACATT?
a. GAGCATT
b. GTGACATT
c. CTCTGATT
d. GATACAGT
5. Which of the following is a point mutation that does not produce a frameshift?
a. substitution
b. insertion
c. deletion
d. inversion
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SHORT ANSWER Answer the questions in the space provided.
1. In humans and fruit flies, which parent determines the sex of the offspring? Explain why.
2. How did Morgan determine that red-eye color in Drosophila is an X-linked trait?
3. Explain why traits that are controlled by genes on the same chromosome do not always appear
in the expected ratio in offspring.
4. Critical Thinking Would a frameshift mutation have a more serious effect if it occurred near
the beginning of a gene or the end of a gene? Explain your answer.
The Drosophila genes for white
eyes, vermilion eyes, and miniature wings are located on the same
chromosome. The table shows
how often these genes are
separated by crossing-over.
0
62
Section 12-1 Review
Genes
Frequency of
crossing-over
Vermilion eyes and miniature wings
3%
White eyes and vermilion eyes
30%
White eyes and miniature wings
33%
40
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STRUCTURES AND FUNCTIONS Use the data in the table below to indicate the position
of these genes on the chromosome map shown below. Assuming that the gene for white
eyes has a chromosome map unit number of 1, write the map unit numbers above each
gene’s position on the chromosome map.
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SEC T I O N 1 2 - 2 R E VIEW
H UMAN G ENETICS
VOCABULARY REVIEW Name a trait or genetic disorder that is caused by each of the
following patterns of inheritance.
1. polygenic inheritance
2. multiple alleles
3. autosomal dominant
4. sex-influenced trait
5. incomplete dominance
MULTIPLE CHOICE Write the correct letter in the blank.
1. Which individual(s) in the pedigree shown below must be a carrier?
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a.
b.
c.
d.
1 only
4 only
3 only
both 1 and 4
1
2
3
4
2. Since the ABO blood group alleles are codominant, an individual with the genotype I AI B
will have blood type
a. A.
b. B.
c. AB.
d. O.
3. Which of the following human traits is not a polygenic trait?
a. skin color
b. eye color
c. height
d. ABO blood type
4. A trait whose expression is affected by the presence of sex hormones is said to be
a. sex-influenced.
b. sex-linked.
c. X-linked.
d. Y-linked.
5. In humans, PKU can be treated by
a. insulin injections.
b. diet.
c. gene therapy.
d. surgery.
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SHORT ANSWER Answer the questions in the space provided.
1. Why is pattern baldness more common in men than in women?
2. Briefly describe how amniocentesis and chorionic villi sampling are used in genetic screening.
3. Explain the difference between a sex-linked trait and a sex-influenced trait.
4. Critical Thinking A couple has four children, and each child has a different ABO blood type.
STRUCTURES AND FUNCTIONS In the two pedigrees below, indicate all possible offspring
in generation II by correctly filling in the male and female symbols for generation II. Use a
completely filled symbol to represent an individual who displays the trait and a half-filled
symbol to represent a carrier.
X-linked recessive trait
Generation I
Generation II
64
Section 12-2 Review
Autosomal recessive trait
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What are the blood types and genotypes of the children and the parents?
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Section 12-1
VOCABULARY REVIEW
1. A sex chromosome contains genes that determine
an individual’s sex. An autosome is a chromosome
that is not directly involved in determining sex.
2. A germ-cell mutation occurs in one of an organism’s
gametes; a somatic-cell mutation occurs in one of
the other cells in an organism’s body.
3. Translocation occurs when a chromosome piece
breaks off and attaches to a nonhomologous
chromosome; nondisjunction occurs when homologues fail to separate during meiosis, so that one
gamete receives both homologues.
4. A deletion is a loss of a piece of chromosome due
to breakage. An inversion occurs when a broken
piece of chromosome is reattached backwards.
5. In a substitution, one nucleotide in a codon is
replaced with a different one; in a frameshift
mutation, the loss or addition of a nucleotide
causes the remaining codons to be incorrectly
grouped.
MULTIPLE CHOICE
1. b
2. a
3. c
4. d
5. a
SHORT ANSWER
1. The male parent determines the offspring’s sex.
Offspring that receive an X chromosome from the
male parent will be female; those that receive a
Y chromosome will be male.
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2. Morgan crossed a white-eyed male with a female
homozygous for red eyes, and then crossed members of the F1 generation resulting from the first
cross. He found that all of the white-eyed flies in
the F2 generation were male.
3. Crossing-over during meiosis causes homologous
chromosomes to exchange alleles, resulting in new
combinations of alleles in the offspring.
4. A frameshift mutation would have a more serious
effect if it occurred near the beginning of a gene,
since it would change nearly all of the codons in
the gene. The resulting protein likely would be
nonfunctional.
STRUCTURES AND FUNCTIONS
white eyes (map unit number 1), vermilion eyes (31),
miniature wings (34)
Section 12-2
VOCABULARY REVIEW
1. skin color, eye color, height, or hair color
2. ABO blood groups
3. Huntington’s disease
4. pattern baldness
5. wavy hair
MULTIPLE CHOICE
1. d
2. c
3. d
4. a
5. b
STRUCTURES AND FUNCTIONS
X-linked recessive trait: one filled square, one open
square, one half-filled circle, and one open circle.
Autosomal recessive trait: one half-filled square,
one open square, one half-filled circle, and one
open circle.
10
Modern Biology Study Guide Answer Key
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SHORT ANSWER
1. Pattern baldness is controlled by the allele B.
Testosterone interacts with the heterozygous
genotype (BB′) to produce baldness. Since males
have higher levels of testosterone, BB′ males are
more likely to lose their hair than BB′ females.
2. A small sample is removed from the amniotic fluid
surrounding the fetus or from the chorionic villi
between the uterus and the placenta. Fetal cells in
the sample are used to construct a karyotype,
which may reveal chromosomal abnormalities.
3. A sex-influenced trait is influenced by the presence of sex hormones and its genes are not located on sex chromosomes, while a sex-linked
trait is linked to a sex chromosome.
4. Children: type A, I Ai; type B, I Bi; type AB, I AI B; type
O, ii. One parent is type A, I Ai; the other parent is
type B, I bi.