Meiosis
Formation of Sex Cells to
Transfer Genetic Information
to the Next Generation
Diploid number of Mitosis and Meiosis in the
Nuclear division
chromosomes,
retaining the original
Human Life Cycle
two full sets
chromosome number
Nuclear division
reducing the
chromosome
number, leading
to sperm or eggs
Haploid number of
chromosomes,
one full set
Mitosis and Meiosis
Human Cell with 46
chromosomes (DIPLOID)
Human Cell with 46
chromosomes (DIPLOID)
Interphase
Mitosis
Cytokinesis
Interphase
Meiosis
Cytokinesis
2 Genetically-Identical
Human Cells each with
46 chromosomes
(DIPLOID)
4 Genetically-Different
Human Cells each with
23 chromosomes
(HAPLOID)
Homologous Chromosome Pairs
• Diploid cells have
pairs of
chromosomes
• Each homologous
chromosome pair is
genetically matched
so that the genes are
arranged in the
same order
• Meiosis distributes
members of each
pair to separate Humans have 1 pair of sex chromosomes
and 22 pairs of autosomes
nuclei
Cell Cycle With Meiosis
Meiosis
G1 = growth phase 1
S = synthesis phase
G2 = growth phase 2
G2
synthesis of
proteins and
assembly of
components
for division
S
chromosomes
duplicate
Interphase includes
cytokinesis
G1
cytoplasm
doubles,
including
organelles
Interphase
Meiosis includes two
chromosomal divisions
Meiosis I
Meiosis II
Cytokinesis = division of
cytoplasmic contents
Applying Your Knowledge
1.
2.
3.
4.
G1 phase
S phase
G2 phase
Meiosis I and II
A. When does chromosomal division occur?
B. When do the cytoplasmic contents double?
C. When does chromosome duplication occur?
Reduction Division:
Separation of homologous
chromosomes, reducing the
chromosome number to
haploid
Equational Division:
Separation of sister
chromatids, no change in
chromosome number
Meiosis Involves Two Chromosomal Divisions
Homologous
Chromosome Pair
Duplicated
chromosomes
joined at their
centromeres
Nonsister Chromatids
are joined to different
centromeres
Duplicated
Chromosomes
in Early Meiosis
Centromere =
constricted region
Prophase I of Meiosis I
Chromosomes thicken
Genetic exchange occurs between nonsister
chromatids through crossing-over
Metaphase I of Meiosis I
Spindle fiber
Homologous pairs line up at the cell equator
Spindle fibers attached to centromeres cause
chromosomal movement
Anaphase I and Telophase I
of Meiosis I
Anaphase I
Members of homologous pair
separate and are pulled to
opposite poles of the cell
Telophase I
Chromosomes reach opposite
poles
Cytokinesis
Cytoplasm divides into two
separate cells
+ cytokinesis
Daughter cells are haploid
with duplicated chromosomes
Prophase II and Metaphase II of
Meiosis II
Prophase II
Chromosomes thicken
Metaphase II
Chromosomes line up
at cell equator
Anaphase II and Telophase II of
Meiosis II
Anaphase II
Sister Chromatids
separate and move to
opposite poles
Telophase II
Chromosomes have
reached opposite poles
Cytokinesis
Cytoplasm divides into
separate cells
+ cytokinesis
Daughter cells are haploid
and have genetic differences
Applying Your Knowledge
1.
2.
3.
4.
5.
Prophase I
Metaphase I
Anaphase I
Metaphase II
Anaphase II
A. When do sister chromatids separate?
B. When does crossing-over occur?
C. When do homologous pairs line up at
the cell equator?
Sperm formation
•Equal divisions of cytoplasm
•Four functional products per meiosis
Fertilization occurs
after Meiosis I and
stimulates Meiosis II
Egg formation
•Unequal divisions of cytoplasm
•Small polar bodies formed
•One functional product per meiosis
Comparing Mitosis and Meiosis
Mitosis
Cell type at start
Cell type at end
Are products identical? (Y/N)
Number of cells produced
Number of chromosome
duplications
Pairing of homologues (Y/N)
Crossing-over (Y/N)
Number of chromosome
divisions
Meiosis
Comparing Mitosis and Meiosis
Mitosis
Cell type at start
Diploid
Cell type at end
Diploid
Are products identical? (Y/N)
Yes
Number of cells produced
2
Number of chromosome
duplications
Pairing of homologues (Y/N)
Crossing-over (Y/N)
Number of chromosome
divisions
Meiosis
Diploid
Haploid
No
4
1
1
No
No
Yes
Yes
1
2