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9
SEXUAL REPRODUCTION
CHAPTER REVIEW
Meiosis is the type of nuclear division that occurs during sexual reproduction. Meiosis is patterned after mitosis
but with several important differences. These are the mechanics of meiosis:
1. Requires two nuclear divisions.
2. Chromosome pairs, each a duplicated
chromosome, separate during the first
division. This reduces the chromosome
number from the full number to half the
number.
3. Separation of sister chromatids is delayed
until the second division.
The function of meiosis is to reduce the chromosome
number during formation of the gametes, the sperm and
egg. When the sperm and egg fuse during fertilization,
the full chromosome is restored.
When nondisjunction occurs, the homologous chromosomes (homologues) have failed to separate during
meiosis II. Nondisjunction leads to gametes with an abnormal number of chromosomes and syndromes in individuals.
CHAPTER KEY TERMS
After studying the key terms of this chapter, match the phrases below with the alphabetized list of terms.
allele
meiosis I
autosome
meiosis II
crossing-over
nondisjunction
diploid (2n) number
oogenesis
haploid (n) number
sex chromosome
homologous chromosome (homologue)
spermatogenesis
interkinesis
tetrad
Klinefelter syndrome
Turner syndrome
a. one of two that are alternative forms of a gene _______________________
b. full number of chromosomes _______________________
c. half the number of chromosomes _______________________
d. first division of meiosis _______________________
e. second division of meiosis _______________________
f. in between the two divisions of meiosis _______________________
g. chromosome that determines the body traits of an individual _______________________
h. chromosome that determines the gender of an individual _______________________
i. formation of sperm _______________________
j. formation of egg _______________________
k. four chromatids in close proximity _______________________
l. exchange of genetic material between nonsister chromatids of a tetrad _______________________
m. one of a pair of like chromosomes _______________________
n. sex chromosomes are XO _______________________
o. sex chromosomes are XXY _______________________
p. homologous chromosomes fail to separate _______________________
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S T U DY E X E R C I S E S
Study the text section by section as you answer the questions that follow.
9.1 THE BASICS
OF
MEIOSIS (PP. 128–131)
• In males and females, the body cells are diploid and have 23 pairs of chromosomes; one pair is the sex
chromosomes.
• The human life cycle includes mitosis (for growth and repair) and meiosis (for the production of gametes).
• The gametes are haploid and have only one chromosome from each pair of chromosomes. Fertilization
restores the number of chromosomes.
• Meiosis produces genetically different gametes. After fertilization, a zygote has a different combination of
chromosomes than either parent.
1. Place an X next to the statements that pertain to the body cells of an individual.
Every body cell in a human has:
a.
the diploid number of chromosomes.
b.
homologous chromosomes (homologues).
c.
11 pairs of autosomes and one chromosome.
2. Label the adjacent diagram
of the human life cycle.
• Label each structure as n
or 2n
• Label the boxes as
meiosis or fertilization
• Label the arrows as
mitosis, oogenesis, or
spermatogenesis
a.
l.l.
b.
c.
d.
d.
k.
zygo
zy
got
ote
te
j.
e.
f.
f.
egg
g.
h.
sp
sper
sperm
perm
i.i
3. During meiosis, homologous chromosomes come together to form a tetrad.
In the following diagram of a tetrad, label sister chromatids, nonsister
chromatids, centromere, and homologous pair:
a.
d.
c.
b.
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4. Pairing of the homologous chromosomes is of upmost importance during meiosis. Why does pairing of the
homologous chromosomes lead to:
a. crossing-over? _________________________________________________________________________________
b. haploid daughter cells? __________________________________________________________________________
c. gametes with different combinations of haploid chromosomes? _______________________________________
d. a constant number of chromosomes in body cells, generation after generation? _________________________
_______________________________________________________________________________________________
5. Use the following diagram of meiosis to answer questions a–g:
What is the diploid number of chromosomes for the cells in the figure?
cell have the diploid or the haploid number of chromosomes?
have the diploid or the haploid number of chromosomes?
correct way to symbolize meiosis.
II?
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b. _______________
c. _______________
Does the parent
Do the final daughter cells
Explain why 2n → n is the
d.
What structures separate during meiosis I?
f.________________________
a. _______________
e. ____________________
What structures separate during meiosis
In humans, meiosis occurs during the production of
g. _____________________.
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6. During interphase prior to meiosis I, synapsis and sometimes crossing-over occur. Using ink for one
duplicated chromosome and pencil for the other, draw a tetrad before and after crossing-over has occurred.
9.2 THE PHASES
OF
MEIOSIS (PP. 132–133)
• Meiosis I and meiosis II have four phases each.
• Following meiosis I, the daughter cells are haploid, and following meiosis II, the chromosomes are no longer
duplicated.
7. a. Draw the stages of meiosis I for the nucleus of a cell whose diploid number is four. Use ink for the
chromosomes inherited from the father and pencil for the chromosomes inherited from the mother.
Meiosis I
7. b. Draw the stages of meiosis II for the nucleus of a cell whose diploid number is four:
Meiosis II
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9.3 MEIOSIS COMPARED TO MITOSIS (PP. 134–135)
• Meiosis reduces the chromosome number during the production of gametes. Mitosis keeps the chromosome
number constant during growth and repair of tissues.
• In humans and many other animals, meiosis is part of the production of sperm in males and eggs in females.
8. Complete the table by writing yes or no to distinguish meiosis from mitosis:
Meiosis
Completed after one division
a.
Requires two successive divisions
b.
During anaphase,
daughter chromosomes separate.
c.
During anaphase I, homologous
chromosomes separate.
d.
Results in daughter cells with the
diploid number of chromosomes
e.
Results in daughter cells with the
haploid number of chromosomes
f.
Unique to the somatic (body) cells
g.
Unique to the sex organs
h.
Mitosis
9. Fill in the blanks with either mitosis or meiosis for questions a–n:
a. _____________________ Occurs when a fertilized egg grows to be a baby in a mother’s womb.
b. _____________________ Occurs when you cut your finger and it heals.
c. _____________________ Occurs in the testes of the male and begins in the ovary of the female.
d. _____________________ diploid → diploid
e. _____________________ diploid → haploid
f. _____________________ Accounts for the fact that no child looks exactly like either parent.
Refer to these drawings to answer questions g and h:
g.
h.
i.
j.
k.
l.
m.
n.
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_____________________
_____________________
_____________________
_____________________
_____________________
_____________________
_____________________
_____________________
Should be associated with the resulting daughter cell on the left in this drawing.
Should be associated with the resulting daughter cell on the right of this drawing.
Daughter cells have exactly the same genes as the parent cell.
Offspring has one-half the genes of the mother or the father.
Daughter cells have two chromosomes of each kind and two genes of each kind.
Daughter cells have one chromosome of each kind and one gene of each kind.
2n → n
2n → 2n
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9.4 ABNORMAL CHROMOSOMES INHERITANCE (PP. 136–137)
• An error during meiosis can produce gametes that have too many or too few chromosomes.
• A person with Down syndrome has three number 21 chromosomes, usually because the egg had two copies
instead of one.
• Turner females are XO, and Klinefelter males are XXY.
10. a. How many chromosomes are in the human karyotype? _________________
b. How many homologous pairs are in the karyotype? _________________
c. (1) How many pairs of sex chromosomes? _________________
(2) What are the sex chromosomes for males? _________________
(3) For females? _________________
d. How many pairs of autosomes are in the karyotype? _________________
e. Which parent determines the gender of the offspring? _________________
11. Fill in these diagrams to show how nondisjunction during meiosis I (left) or meiosis II (right) could bring
about an egg that contains two chromosomes 21, and therefore Down syndrome:
Meiosis I
Meiosis I
Meiosis II
normal meiosis I
nondisjunction
Gamete
pair of
homologous
chromosomes
Meiosis II
nondisjunction
Gamete
pair of
homologous
chromosomes
normal meiosis II
Gamete
Nondisjunction during meiosis II
Nondisjunction during meiosis I
12.
Gamete
Complete the following table.
Name
Chromosome Abnormality
Description
a. Down syndrome
b. Turner syndrome
c. Klinefelter syndrome
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D E F I N I T I O N S WO R D S E A R C H
Review key terms by searching for the following alphabetized list of terms and filling in the blanks below:
S
A
U
T
O
S
O
M
E
B
S
E
W
E
D
P
T
R
P
G
S
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A
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I
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I
M
I
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A
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Y
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B
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O
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R
H
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N
D
A
Y
D
I
O
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M
O
A
A
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I
J
G
N
A
M O
D W
P S
F L
R B
U J
P L
H S
E N
I K
T O
L
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O
K
O
I
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O
F
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T
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F
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N
S
D
C
S
autosome
Barr body
diploid
haploid
homologue
interkinesis
meiosis
oogenesis
spermatogenesis
synapsis
a. _____________________
Structure found in the nuclei of female mammals.
b. _____________________
Cell division resulting in cells with half as many chromosomes as the parental cell.
c. _____________________
Process of egg production in females.
d. _____________________
Process of sperm production in males.
e. _____________________
Chromosome other than a sex chromosome.
f. _____________________
Period of time between meiosis I and meiosis II.
g. _____________________
Member of a homologous pair of chromosomes.
h. _____________________
Pairing of homologous chromosomes during prophase I.
i. _____________________
Half the usual number of chromosomes.
j. _____________________
The normal full complement of chromosomes.
CHAPTER TEST
OBJECTIVE QUESTIONS
Do not refer to the text when taking this test.
1. Who determines the sex of the offspring?
a. male
b. female
c. both male and female
d. alternately male, then female
2. Autosomes
a. determine sex of individual.
b. are nonsex chromosomes.
c. refer to human chromosomes.
d. are abnormal chromosomes.
3. The genes that cause Down syndrome are
a. on chromosome 21.
b. associated with Down syndrome.
c. associated with mental retardation.
d. All of these are correct.
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4. Which statement is true for both genes and
chromosomes?
a. come in pairs
b. separate during meiosis
c. all possible combinations in gametes
d. Gametes have one-half the total number.
e. All of these are correct.
5. Which of these is true of meiosis?
a. n → n
b. n → 2n
c. 2n → n
d. 2n → 2n
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6. If a parent cell has 56 chromosomes, following
mitosis each daughter cell will have ___________
chromosomes.
a. 14
b. 28
c. 56
d. The number cannot be determined.
7. The zygote
a. is produced by fertilization.
b. is diploid.
c. undergoes mitosis.
d. All of these are correct.
8. Synapsis is associated with
a. crossing-over.
b. mitosis.
c. meiosis II.
d. All of these are correct.
9. Which of these is 2n → 2n?
a. mitosis
b. meiosis
c. oogenesis
d. spermatogenesis
10. The following drawing could represent a stage
only in the process of
a. meiosis I.
b. meiosis II.
c. mitosis.
d. oogenesis.
e. meiosis I and oogenesis.
11. By the end of meiosis I,
a. crossing-over has occurred.
b. chromatids of each chromosome have separated.
c. synapsis of homologous chromosomes has
occurred.
d. each cell produced is genetically identical to the
original cell.
e. Both a and c are correct.
12. During which stage do tetrads line up at the equator of the spindle?
a. mitosis–metaphase
b. meiosis–metaphase I
c. meiosis–metaphase II
d. Both b and c are correct.
13. Meiosis
a. keeps genetic makeup constant.
b. is involved in the cell cycle.
c. assures chromosomal variations.
d. prevents chromosomal variations.
14. Nondisjunction is the
a. exchange of chromosome pieces.
b. loss of a piece of chromosome.
c. repeating of the same piece of a chromosome.
d. failure of chromosome pairs to separate completely.
15. During anaphase of meiosis II,
a. homologues separate.
b. daughter chromosomes separate.
c. daughter centrioles separate.
d. duplicated chromosomes separate.
16. By the end of meiosis I,
a. crossing-over has occurred.
b. daughter chromosomes have separated.
c. synapsis of homologues has occurred.
d. each daughter nucleus is genetically identical to the original cell.
e. Both a and c are correct.
CRITICAL THINKING QUESTIONS
The introduction to this chapter discusses how meiosis differs between males and females.
17. What is the function of meiosis in the human life cycle? _____________________________________________________
18. What is gametogenesis (production of gametes) called in males and in females? ______________________________
19. Where do you predict spermatogenesis occurs? ______________________________________________________________
20. Where do you predict oogenesis occurs? ____________________________________________________________________
21. What is another function of meiosis? ________________________________________________________________________
How might this help evolution? _____________________________________________________________________________
Test Results: ______ number correct ÷ 21 = ______ × 100 = ______ %
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EXPLORING
THE
INTERNET
ARIS, the Essentials of Biology website: http://www.mhhe.com/essentials
ARIS, the website for Essentials of Biology, offers access to a wide variety of tools to help students learn biological
concepts and to reinforce their knowledge. Online study aids such as practice quizzes, interactive activities, animations, labeling exercises, flashcards, and much more are organized according to the major sections of each chapter.
There is even an online tutorial service!
ANSWER KEY
CHAPTER KEY TERMS
a. allele b. diploid (2n) number c. haploid (n) number
d. meiosis I e. meiosis II f. interkinesis g. autosome
h. sex chromosome i. spermatogenesis j. oogenesis
k. tetrad l. crossing-over m. homologous chromosome
n. Turner syndrome o. Klinefelter syndrome p. nondisjunction
STUDY EXERCISES
1. a. mitosis b. 2n c. 2n d. 2n e. meiosis f. oogenesis
g. n h. spermatogenesis i. n j. fertilization k. 2n l. mitosis 3. a. nonsister chromatids b. homologous pair
c. centromere d. sister chromatids 4. a. The nonsister
chromatids get close enough to exchange genetic material. b. Homologous chromosomes (homologues) can
now separate from one another. c. There are no restrictions to which of the homologous chromosomes (homologues) got to which daughter nucleus. d. Because the
gametes are haploid. Zygotes are diploid following fertilization. 5. a. four b. diploid c. haploid d. Parent
cell is 2n and daughter cells are n. e. homologous chromosomes f. chromatids g. gametes 6. See Fig. 9.4, page
131, in text. 7. a. See Fig. 9.5, page 132, in text. b. See
Fig. 9.6, page 133, in text. 8. a. no; yes b. yes; no c. no;
yes d. yes; no e. no; yes f. yes; no g. no; yes h. yes;
no 9. a. mitosis b. mitosis c. meiosis d. mitosis e. meiosis f. meiosis g. meiosis h. mitosis i. mitosis j. meiosis k. mitosis l. meiosis m. meiosis n. mitosis
10. a. 46 b. 23 c. (1) one (2) XY (3) XX d. 22 e. male
parent 11. See Fig. 9.8, page 136, in text. 12. a. extra
chromosome 21; short stature, fold of upper eyelids, large
fissured tongue, round head, mental retardation b. single X; short, broad stature, ovaries are nonfunctional
c. two or more X chromosomes and a Y; sterile, testes underdeveloped, breast development
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DEFINITIONS WORDSEARCH
H OM O L OG
A
S Y N A P S I S
L
B A R R B O D Y
I
D I P L O I D
S I S O
O O G E N E S I
S I S E N I K R E T
S P E R M A T O G E N
A
U
T
O
S
O
M
E
U E
I E M
S
N I
E S I S
a. Barr body b. meiosis c. oogenesis
esis e. autosome f. interkinesis
h. synapsis i. haploid j. diploid
d. spermatogeng. homologue
CHAPTER TEST
1. a 2. b 3. d 4. e 5. c 6. c 7. d 8. a 9. a
10. e 11. e 12. b 13. c 14. d 15. b 16. e 17.
reduces chromosome number during gamete production 18. spermatogenesis and oogenesis 19. in the
testes of males 20. in the ovaries of females 21. production of offspring that carry a different combination of
genes than their parents. Some combinations of genes
might be more suited to the environment than other combinations.