1028
UNIT 5
Continuity
27
MITOSIS
MEIOSIS
MITOSIS
MEIOSIS
Mother cell
(before chromosome replication)
Replicated
chromosome
Tetrad formed by
synapsis of
replicated homologous
chromosomes
Tetrads align randomly
at the metaphase plate
Homologous chromosomes
separate but sister chromatids
remain together during anaphase I
No further chromosomal
replication; sister chromatids
separate during anaphase II
One, consisting of prophase, metaphase,
anaphase, and telophase.
Number of
divisions
Synapsis of
homologous
chromosomes
Daughter cell
number and
genetic
composition
Roles
in the body
Two, each consisting of prophase, metaphase, anaphase, and telophase.
DNA replication does not occur between the two nuclear divisions.
Does not occur.
Occurs during prophase I; tetrads form, allowing crossovers.
Two. Each diploid (2
n
) cell is identical to
the mother cell.
Four. Each haploid (
n
) cell contains half as many chromosomes as the
mother cell and is genetically different from the mother cell.
For development of multicellular adult from
zygote. Produces cells for growth and tissue
repair as multicellular adult develops. Ensures
genetic makeup of all body cells is constant.
Produces cells for reproduction (gametes). Introduces genetic variability
in the gametes and reduces chromosomal number by half so that when
fertilization occurs, the normal diploid chromosomal number is restored
(in humans, 2
n
=
46).
Daughter cells of meiosis II
(usually gametes)
n
n
n
n
Chromosome
replication
Chromosome
replication
2
n
=
4
Prophase
Prophase I
Metaphase I
Daughter cells
of Meiosis I
Meiosis II
Chromosomes
align at the
metaphase plate
Sister chromatids separate
during anaphase
2
n
2
n
Metaphase
Daughter
cells of
mitosis
Figure 27.6
Comparison of mitosis and meiosis in a mother cell with a diploid
number (2
n
) of 4.
(Not all the phases of mitosis and meiosis are shown, and only one possible
alignment of the tetrads at metaphase I is illustrated.)
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