100 µm
20 µm
200 µm
(b) Growth and
development
(a) Reproduction
(c) Tissue renewal
20 µm
1
0.5 µm
Chromosomes
Chromosome arm
Centromere
2
DNA molecules
Chromosome
duplication
(including DNA
synthesis)
G2 of Interphase
Prophase
Centrosomes
Chromatin
(with centriole (duplicated)
pairs)
Sister
chromatids
Separation of
sister chromatids
Early mitotic Aster Centromere
spindle
Nucleolus Nuclear Plasma
envelope membrane
Chromosome, consisting
of two sister chromatids
Metaphase
Prometaphase
Fragments Nonkinetochore
of nuclear
microtubules
envelope
Kinetochore
Kinetochore
microtubule
Anaphase
Spindle
Centrosome at
one spindle pole
Telophase and Cytokinesis
Cleavage
furrow
Metaphase
plate
Daughter
chromosomes
Nucleolus
forming
Nuclear
envelope
forming
Centromere
Sister chromatids
3
4
5 µm
Key
Pair of homologous
replicated chromosomes
2n = 6
Maternal set of
chromosomes (n = 3)
Paternal set of
chromosomes (n = 3)
Centromere
Two sister chromatids
of one replicated
chromosome
Sister
chromatids
Two nonsister
chromatids in
a homologous pair
Metaphase
chromosome
5
Centromere
Pair of homologous
chromosomes
(one from each set)
6
Key
Haploid gametes (n = 23)
Haploid (n)
Egg (n)
Diploid (2n)
Key
Haploid (n)
MEIOSIS
Gametes
n
FERTILIZATION
n
Mitosis
n
n
Testis
Zygote
2n
Diploid
zygote
(2n = 46)
Diploid
multicellular
organism
Mitosis
n
n
Spores
MEIOSIS
Ovary
Mitosis
n
n
FERTILIZATION
MEIOSIS
Haploid unicellular or
multicellular organism
Haploid multicellular organism
(gametophyte)
Diploid (2n)
Sperm (n)
Mitosis
n
n
n
n
Gametes
Gametes
MEIOSIS
2n
2n
2n
Diploid
multicellular
organism
(sporophyte)
Mitosis
(a) Animals
n
FERTILIZATION
Zygote
FERTILIZATION
2n
Mitosis
Zygote
(c) Most fungi and some protists
(b) Plants and some algae
Mitosis and
development
Multicellular diploid
adults (2n = 46)
7
8
Interphase
Homologous pair of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Metaphase I
Prophase I
Sister
chromatids
Sister
chromatids
Chiasmata
Diploid cell with
replicated
chromosomes
Spindle
Telophase I and
Cytokinesis
Anaphase I
Centrosome
(with centriole pair)
Prophase II
Centromere
(with kinetochore)
Homologous
chromosomes
separate
Homologous
chromosomes
1 Homologous
chromosomes
separate
Anaphase II
Telophase II and
Cytokinesis
Metaphase
plate
Meiosis I
Fragments
of nuclear
envelope
Metaphase II
Sister chromatids
remain attached
Sister chromatids
separate
Cleavage
furrow
Haploid daughter cells
forming
Microtubule
attached to
kinetochore
Haploid cells with
replicated chromosomes
Meiosis II
2 Sister chromatids
separate
Haploid cells with unreplicated chromosomes
9
MITOSIS
MEIOSIS
Parent cell
Chromosome
replication
Prophase
10
Chiasma
Chromosome
replication
Possibility 2
Possibility 1
Prophase I
Two equally probable
arrangements of
chromosomes at
metaphase I
Homologous
chromosome
pair
2n = 6
Replicated chromosome
MEIOSIS I
Metaphase I
Metaphase
Metaphase II
Anaphase
Telophase
Daughter
cells of
meiosis I
2n
Daughter cells
of mitosis
2n
Anaphase I
Telophase I
Haploid
n=3
Daughter
cells
Combination 1 Combination 2
MEIOSIS II
Combination 3 Combination 4
n
n
n
n
Daughter cells of meiosis II
11
12
Fig. 15-13-3
Prophase I
of meiosis
Pair of
homologs
Nonsister
chromatids
held together
during synapsis
Meiosis I
Chiasma
Nondisjunction
Meiosis II
Centromere
TEM
Anaphase I
Nondisjunction
Gametes
Anaphase II
n+1
n+1
n–1
n–1
n+1
n–1
n
n
Number of chromosomes
Daughter
cells
Recombinant chromosomes
(a) Nondisjunction of homologous
chromosomes in meiosis I
13
(b) Nondisjunction of sister
chromatids in meiosis II
14