Download Meiosis

Do-Now: Review from Mitosis
•
A human body cell has 46
chromosomes. In a human body cell,
mitosis produces
A) two cells with 46 chromosomes in each.
B) two cells with 23 chromosomes in each.
C) four cells with 23 chromosomes in each.
D) four cells with 46 chromosomes in each.
Do-Now: Review from Mitosis
•
A human body cell has 46
chromosomes. In a human body cell,
mitosis produces
A) two cells with 46 chromosomes in each.
B) two cells with 23 chromosomes in each.
C) four cells with 23 chromosomes in each.
D) four cells with 46 chromosomes in each.
Mitosis Review
• In mitosis, a parent body cell
divides to make two
daughter body cells
• New daughter cells are
diploid…have two sets of
chromosomes (46 total in
humans)
• Example: one blood cell
divides to make two blood
cells
Mitosis Review
Only DIPLOID cells are made in mitosis
Diploid
Haploid
Sets of Chromosomes 2
1
Total # of
chromosomes in
humans
46
23
Type of Cell
Body cell (ex,
Sex cell (sperm
blood cell, bone or egg cell)
cell)
Meiosis- A New Type of
Division
1) During meiosis, new SEX
CELLS (eggs and sperm)
are created.
2) Eggs and sperm are
haploid, meaning they
have one set of
chromosomes (23 total).
Why might it be a problem for sex cells to be diploid
?
Meiosis
• A process where the nucleus divides that splits
the original chromosomes into haploid daughter
cells
Human Body Cell = 46
Egg or Sperm Cell = 23
• Why?... so that chromosome number won’t be
doubled during fertilization
• Key Point: Meiosis makes fertilization
possible!!!
Types of Reproduction
1. Asexual = makes
offspring (children) that
are identical to the
parent (ex: binary fission
in bacteria or “budding”
in sponges)
2. Sexual = makes offspring
that are different from
the parent, meiosis
happens and then
sperm and egg join
Stages
• Before meiosis begins: Interphase (G1,
S, G2)
• What happens during each part of
interphase? Is this considered part of cell
division?
• During Meiosis:
-Meiosis I
-Meisis II
Remember the Cell Cycle?
Meiosis uses the
same cycle as
mitosis, except
meiosis happens in 2
parts.
Interphase must still
happen so the cell
can grow, copy its
DNA, and prepare for
division.
Meiosis I
• Chromosome number gets cut in half
(1 diploid cell  2 haploid cells)
• 4 parts
1) Prophase I
2) Metaphase I
3) Anaphase I
4) Telophase I
Prophase I
Similarities to Mitosis:
• DNA coils into chromosomes
• Spindle fibers are made
• Nuclear Membrane breaks down
Prophase I
• Differences from Mitosis
• Homologous chromosomes pair up
• Homologous chromosomes = pairs of
chromosomes (1 from mother and 1 from
father) that have the same genes (ex:
gene for eye color)
Prophase I: Crossing Over
• Crossing over =
homologous
chromosomes “trade”
genes
• Results in Genetic
Recombination
• Tetrad = the pair of
chromosomes
Why does crossing over take
place?
• Trades genes so that offspring look
different from either parent and from their
siblings.
Prophase I
Label:
1) Homologous
Chromosomes
2) Nuclear
Membrane
3) Spindle
4) Crossing Over
Metaphase I
•
•
Tetrads line up in the
middle of the cell
Spindle fibers attach
to the chromosomes
Label: Homologous
Chromosomes,
Centromere, Spindle,
Metaphase Plate
Anaphase I
• Homologous
Chromosomes move to
opposite ends of the cell
Label: Homologous
chromosomes, spindle
Telophase I and Cytokinesis
• Chromosomes reach
opposite ends
• Cytoplasm divides
• End Result = 2 daughter
cells with half the original
chromosome number
Label: Nuclear membrane,
centrioles, chromosomes
Meiosis II
• DNA is NOT copied again
• Chromatids (identical copies of DNA)
separate like they do during mitosis
• 4 Stages:
1) Prophase II
2) Metaphase II
3) Anaphase II
4) Telophase II and Cytokinesis
Meiosis II
End Result of Meiosis: 4 haploid daughter cells
Prophase II
• Nuclear membrane
breaks down
• Spindle is made
Label: Nuclear
membrane, spindle,
chromosomes
Metaphase II
• Spindle fibers move
chromosomes to the
center of the cell
Label: Chromosomes,
Chromatids,
Centromere, Spindle,
Metaphase Plate
Anaphase II
• Chromatids of each
chromosome separate
at the centromere and
move toward opposite
ends of the cell
Label: New
Chromosomes, Spindle
Telophase II and Cytokinesis
• Spindle breaks down
• Chromosomes uncoil
Nuclear envelopes form
• Cytoplasm divides
Label: Nuclear
Membrane, Centrioles,
Uncoiling Chromosomes
(chromatin)
Main Goal: Making Sex Cells!
• Gametes = haploid reproductive cells
made during meiosis (ex: sperm and egg)
• Sex cells are made in the testes and
ovaries in humans
Spermatogenesis
• The process of making
sperm cells
• Diploid cell divides by
meiosis to form four
haploid sperm cells
Spermatogenesis
Oogenesis
• The process of making
egg cells
• A diploid cell divides by
meiosis to make ONE
mature egg cell
• Other three haploid
cells = polar bodies
Oogenesis
• Egg gets all the cytoplasm and organelles,
polar bodies are tiny little structures with
DNA only
• Polar bodies break down and die 
Warm Up
1.
2.
3.
What does it mean to be a diploid cell?
How does meiosis make fertilization possible?
What are three ways in which asexual reproduction is different
from sexual reproduction?
4. Is Interphase considered part of cell division?
5. How does crossing over contribute to genetic variability?
6. How is the end result of meiosis different from the end result of
mitosis?
7. How is the one egg cell different from the three polar bodies?
8. What is the main difference between spermatogenesis and
oogenesis?
9. How is Prophase 1 of meiosis and Prophase of mitosis different?
10. Which part of meiosis (meiosis 1 or meiosis 2) is most like mitosis?
Meiosis Poster: 8 Section, Label Phases, Draw Diagrams, Describe what is
Going on at each phase, Label. Use COLOR. Follow Chromosomes.
Prophase 1 Label: Homologous Chromosomes, Centrioles, Nuclear Membrane,
Sister Chromatids, Spindle Fibers, Tetrad, Crossing Over
Metaphase 1 Label: Homologous Chromosomes, Centrioles, Centromere,
Spindle Fibers, Metaphase Plate, Sister Chromatids
Anaphase 1 Label: Homologous Chromosomes, Centrioles, Sister
Chromatids, Spindle Fibers
Telophase 1 Label: Nuclear membrane, Centrioles, Spindle Fibers, Homologous
Chromosomes, Sister Chromatids
Prophase 2 Label: Nuclear membrane, Spindle Fibers, Centriole, Homologous
Chromosomes, Sister Chromatids
Metaphase 2 Label: Homologous Chromosomes, Sister Chromatids,
Centromere, Spindle Fibers, Centrioles, Metaphase Plate
Anaphase 2 Label: Nuclear Membrane, Centrioles, Sister Chromatids,
Spindle Fibers
Telophase 2 Label: Nuclear Membrane, Centrioles, Uncoiling Sister Chromatids
(chromatin), Spindle Fibers
Don’t Forget to Label Diploid and Haploid
• On a separate sheet of paper
compare/contrast Mitosis and Meiosis
(I can come up with at least 15. . . . How
about you?)
DUE Wednesday!! Have a
WONDERFUL Break 