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Bell Work
• Draw a picture of each stage of mitosis.
Intro to Biology - Lecture 36
Meiosis
Meiosis
• A special type of cell division necessary for
sexual reproduction in eukaryotes.
What Cells are Involved
• The cells produced by meiosis are gametes
(sperm and eggs) or spores.
Different from Mitosis
• The chromosomes in meiosis undergo a
recombination which shuffles the genes
producing a different genetic combination in
each gamete
Different from Mitosis
• The outcome of meiosis is four (genetically
unique) haploid cells, compared with the two
(genetically identical) diploid cells produced
from mitosis
The Process of Meiosis
• One cell containing two copies of each
chromosome—one from the mom and one
from the dad - produces four haploid cells
containing one copy of each chromosome.
The End Result of Meiosis
• Resulting chromosomes in the cells are a
unique mixture of DNA from the mom and
dad, resulting in offspring that are genetically
distinct from either parent.
• This makes the organisms unique.
Meiosis
The Full Process of Meiosis
• Interphase I, Meiosis I, Meiosis II
Inperphase
• This creates 2 copies of each chromosome
(one from the mother and one from the
father).
Prophase 1
• The same chromosomes from the mother and
father pair up and exchange parts by a process
called homologous recombination.
• The new pair of chromosomes are called
homologs.
Metaphase I
• Spindle fibers bind to the centromeres of each
pair of homologs and arrange the pairs at the
center of the cell.
Anaphase I
• Then the fibers pull the recombined homologs
to opposite poles of the cell.
Telephase I
• As the chromosomes move away from the
center, a new nucleus is formed.
Cytokinesis
• The cell divides into two daughter cells, each
containing a half number of chromosomes
composed of two chromatids.
Meiosis II
• After the homologs have separated into the
two daughter cells, a second round of cell
division occurs.
Prophase II
• Chromosomes prepare to line up in the
middle.
• Consists of decoupling each chromosome's
sister strands (chromatids).
Metaphase II
• Chromosomes line up in the middle.
Anaphase II
• Sister chromatids are pulled to opposite sides
of the cell.
Telophase II
• New nuclei form around chromatids
Cytokinesis
• The cell divides.
• The two sister chromatids making up each
homolog are separated and move into one of
the four resulting gamete cells.
When Does it Become a Full Cell Again?
• Upon fertilization, two gamete cells produced
by meiosis fuse.
• The gamete from the mother and the gamete
from the father each contribute one half of
the set of chromosomes that make up the
new offspring's genome.
• Meiosis I and II are each divided into
prophase, metaphase, anaphase, and
telophase stages (like mitosis).
• Meiosis includes the stages of meiosis I
(prophase I, metaphase I, anaphase I,
telophase I), and meiosis II (prophase II,
metaphase II, anaphase II, telophase II).
What undergoes Meiosis?
• Meiosis occurs in eukaryotic life cycles
involving sexual reproduction, consisting of
the constant cyclical process of meiosis and
fertilization.
Meiosis Flipbook
Meiosis
Mitosis
End result
Four cells, each with half the
number of chromosomes as
the parent
Two cells, Having equal
number of chromosomes as
the parent
Function
Sexual reproduction,
production of gametes (sex
cells)
Cellular reproduction, growth,
repair, asexual reproduction
Where does it happen?
Animals, fungi, plants, protists
All eukaryotic organisms
Steps
Prophase I, Metaphase I,
Anaphase I, Telophase I,
Prophase II, Metaphase II,
Anaphase II, Telophase II
Prophase, Metaphase,
Anaphase, Telophase
Genetically same as parent?
No
Usually
Crossing over happens?
Yes, in Prophase I
Sometimes
Pairing of homologous
chromosomes?
Yes
No
Cytokinesis
Occurs in Telophase I and
Telophase II
Occurs in Telophase
Centromeres split
Does not occur in Anaphase I,
but occurs in Anaphase II
Occurs in Anaphase