Cell reproduction, or cell division, produces two daughter cells that are genetically identical to the parent cell. During cell division, the parent cell duplicates its chromosomes and distributes one copy to each daughter cell. This ensures that each daughter cell has the full complement of genetic information. Cell division allows for growth, tissue repair, and asexual reproduction. Sexual reproduction involves meiosis, which produces gametes like eggs and sperm that each contain half the number of chromosomes. When a gamete from each parent joins during fertilization, a new individual is formed with a unique combination of genes from both parents. This genetic variation contributes to evolution in species.
15. Number of chromosomes
in body cells
Indian muntjac deer
Species
Opossum
Koala
Human
Mouse
Giraffe
Buffalo
Dog
Red viscacha rat
Duck-billed platypus
102
78
60
54
46
40
30
22
16
6
Figure 8.2
39. A tumor grows
from a single
cancer cell.
Cancer cells invade
neighboring tissue.
Metastasis: Cancer
cells spread through
lymph and blood
vessels to other parts
of the body.
Glandular
tissue
Blood
vessel
Tumor
Lymph
vessels
Figure 8.9
57. MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE
Sister chromatids
remain attached
Pair of
homologous
chromosomes
INTERPHASE
Sister
chromatids
Homologous
chromosomes
pair up and
exchange
segments.
Chromosomes
duplicate.
Pairs of
homologous
chromosomes
line up.
Pairs of
homologous
chromosomes
split up.
Nuclear
envelope
Chromatin
Centromere
Microtubules
attached
to chromosome
Sites of
crossing over
Spindle
Centrosomes
(with centriole
pairs)
PROPHASE I METAPHASE I ANAPHASE I
Figure 8.14a
58. TELOPHASE II
AND
CYTOKINESIS
Sister
chromatids
separate
ANAPHASE II
Cleavage
furrow
TELOPHASE I
AND
CYTOKINESIS
Two haploid
cells form;
chromosomes
are still
doubled.
MEIOSIS II: SISTER CHROMATIDS SEPARATE
PROPHASE II METAPHASE II
During another round of cell division, the sister
chromatids finally separate; four haploid
daughter cells result, containing single
chromosomes.
Haploid
daughter
cells forming
Figure 8.14b
63. Duplicated chromosome
(two sister chromatids)
MITOSIS
Prophase
Chromosome
duplication
Chromosomes
align at the
middle of the
cell.
Metaphase
Sister
chromatids
separate
during
anaphase.
Anaphase
Telophase
Daughter cells
of mitosis
2n2n
Prophase I
Metaphase I
Anaphase I
Telophase I
MEIOSIS
Chromosome
duplication
Homologous
chromosomes come
together in pairs.
MEIOSIS I
Site of crossing over
between homologous
(nonsister) chromatids
Homologous pairs
align at the middle
of the cell.
Chromosome with two
sister chromatids
Homologous
chromosomes
separate during
anaphase I;
sister chromatids
remain together.
Daughter
cells of meiosis I
Sister chromatids
separate during
anaphase II.
Haploid
n 2
MEIOSIS II
Parent cell
(before chromosome duplication)
2n 4
Daughter cells of meiosis II
n n n n
Figure 8.15
64. Duplicated chromosome
(two sister chromatids)
MITOSIS
Prophase
Chromosome
duplication
Chromosomes
align at the
middle of the
cell.
Metaphase
Prophase I
Metaphase I
MEIOSIS
Chromosome
duplication
Homologous
chromosomes come
together in pairs.
MEIOSIS I
Site of crossing
over between
homologous
(nonsister)
chromatids
Homologous
pairs align at
the middle
of the cell.
Parent cell
(before chromosome duplication)
2n 4
Figure 8.15a
71. Metaphase of
meiosis I
Metaphase
of meiosis II
Combination a
POSSIBILITY 1 POSSIBILITY 2
Combination b Combination c Combination d
Gametes
Figure 8.16-3
75. Metaphase I
Homologous chromatids
exchange corresponding
segments.
Sister chromatids
remain joined at their
centromeres.
Prophase I
of meiosis
Duplicated pair of
homologous
chromosomes
Chiasma, site of
crossing over
Spindle
microtubule
Figure 8.18-3
76. Metaphase I
Metaphase II
Homologous chromatids
exchange corresponding
segments.
Sister chromatids
remain joined at their
centromeres.
Prophase I
of meiosis
Duplicated pair of
homologous
chromosomes
Chiasma, site of
crossing over
Spindle
microtubule
Figure 8.18-4
77. Metaphase I
Metaphase II
Recombinant chromosomes
Gametes
Recombinant
chromosomes
combine genetic
information from
different parents.
Homologous chromatids
exchange corresponding
segments.
Sister chromatids
remain joined at their
centromeres.
Prophase I
of meiosis
Duplicated pair of
homologous
chromosomes
Chiasma, site of
crossing over
Spindle
microtubule
Figure 8.18-5
80. Meiosis I
Nondisjunction:
Pair of homologous
chromosomes fails
to separate.
NONDISJUNCTION IN MEIOSIS I NONDISJUNCTION IN MEIOSIS II
Figure 8.20-1
81. Meiosis I
Nondisjunction:
Pair of homologous
chromosomes fails
to separate.
NONDISJUNCTION IN MEIOSIS I
Meiosis II
Nondisjunction:
Pair of sister
chromatids
fails to separate.
NONDISJUNCTION IN MEIOSIS II
Figure 8.20-2
82. Meiosis I
Abnormal gametes
Gametes
Nondisjunction:
Pair of homologous
chromosomes fails
to separate.
NONDISJUNCTION IN MEIOSIS I
Number of
chromosomes
Meiosis II
Nondisjunction:
Pair of sister
chromatids
fails to separate.
Abnormal gametes Normal gametes
nnn 1n 1 n – 1n 1
NONDISJUNCTION IN MEIOSIS II
n – 1 n – 1
Figure 8.20-3