Bellwork 12/14
The illustration below represents a cell that is
entering mitosis.
1. Identify one function of mitosis.
The cell shown in the illustration has recently completed the
synthesis phase (S phase) of the cell cycle and is in prophase
of mitosis.
2. What happened in this cell during the S phase in
preparation for division? Describe the evidence that
supports your answer.
3. In your Student Answer Booklet, draw the end
products that will be formed when this cell
completes mitosis.
HW- vocabularyuse CH 11 to define these terms.
• Homologous
chromosomes
• Tetrad
• Crossing over
• Trait
• Gene
• Allele
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•
•
•
•
•
Hybrid
Homozygous
Heterozygous
Phenotype
Genotype
Probability
Agenda 12/14- Meiosis
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Bellwork- open response
Finish video- Life’s Greatest Video
Notes- meiosis
HW- vocabulary
Eukaryotic Cell Division
• Mitosis- somatic (non-reproductive) cell division
– Parent cell divides into two identical daughter cells
(diploid=2n)
• Meiosis- cell division resulting in reproductive
cells (gametes)
– Parent cell divides into 4 daughter cells, each with
half the number of chromosomes (haploid=1n)
Bellwork 12/15
Agenda 12/15- Meiosis vs. Mitosis
• Bellwork
• New Information: Meiosis
• Activity:
– Modeling Crossing Over
– Card sort: Mitosis vs. Meiosis
– Vocab Squares: cell division and reproduction
• HW: Dog Named Spot
Eukaryotic Cell Division
• Mitosis- somatic (non-reproductive) cell division
– Parent cell divides into two identical daughter cells
(diploid=2n)
• Meiosis- cell division resulting in reproductive
cells (gametes)
– Parent cell divides into 4 daughter cells, each with
half the number of chromosomes (haploid=1n)
Cell Division
• Humans have 46 chromosomes, 23 from
each parent.
• Haploid cells: only one of each
chromosome (n)
• Diploid cells: two of each chromosome (2n)
Why don’t you look exactly like
your parents or siblings?
• Meiosis!
• Instead of 2 cells that are identical to the
parent cell, as in mitosis, meiosis results in 4
haploid cells that are different from the parent
cell and from each other.
Why don’t you look exactly like
your parents or siblings?
• Meiosis!
• Sexual reproduction increases genetic
variation in a population, which increases a
species’ ability to adapt to changes in their
environment.
Sexual Reproduction
• Male gamete (sperm) and female gamete
(egg) are haploid (1n)
• Fertilization occurs when an egg and a sperm
fuse to form a zygote (2n).
• Meiosis is the form of cell division that results
in gametes.
Meiosis
produces gametes
• 4 haploid daughter cells formed
• Preceded by interphase and DNA replication
• 2 divisions
– Meiosis I
– Meiosis II
Meiosis- click for video clip
• Meiosis I- reduction division; like mitosis but only one
copy of each homologous chromosome goes to each new cell;
two new cells formed
– Prophase I
– Metaphase I- homologous chromosomes line up on
equator to form a tetrad; crossing over occurs
– Anaphase I- homologous chromosomes separate
– Telophase I- two new cells, each with half the genetic
material
• Meiosis II- the two cells formed in Meiosis I divide again, with sister
chromatids separating
– Basically like Mitosis
The Human Karyotype
Homologous Chromosomes
chromosome pair, one
from each parent, that
are similar in length,
gene position and
centromere location
Meiosis I - Reduction Division
Interphase I
Cells undergo a
round of DNA
replication, forming
duplicate
Chromosomes.
Prophase I
Each
chromosome
pairs with its
corresponding
homologous
chromosome
to form a
tetrad.
Metaphase I
Homologous
chromosomes line up
along the middle of the
cell.
Spindle fibers attach to
the chromosomes.
Anaphase I
The fibers pull the
homologous
chromosomes toward
the opposite ends of
the cell.
Meiosis I - Reduction Division
Interphase I
Cells undergo a
round of DNA
replication,
forming duplicate
Chromosomes.
Prophase I
Crossing over-
Metaphase I
Homologous
chromosomes line
up along the middle
of the cell.
exchange of
genes betweenSpindle fibers attach
to the
homologous chromosomes.
chromosomesincreases
genetic variation
among offspring
Anaphase I
The fibers pull the
homologous chromosomes
toward the opposite ends of
the cell.
This reduces the
chromosome
number in each
daughter cell by
half.
Meiosis II - Similar to Mitosis
Prophase II
Meiosis I results in two
haploid (N) daughter
cells, each with half the
number of
chromosomes as the
original.
Metaphase II
The chromosomes line
up in a similar way to
the metaphase stage of
mitosis.
Anaphase II
The sister chromatids
separate and move
toward opposite ends
of the cell.
Telophase II
Meiosis II results in four
haploid (N) daughter
cells.
Modeling Crossing Over
• Use the paper to create a model of crossing
over
• First, draw a pair of duplicated homologous
chromosomes using two different colors.
• Model how the homologous chromosomes
separate during Meiosis I
• Model how the sister chromatids separate
during Meiosis II
Mitosis vs. Meiosis
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Animation
Mitosis- 2 diploid cells produced
Meiosis- 4 haploid cells produced
Why?
Comparing Mitosis and Meiosis
• Place the cards in order
• How are the two processes similar? How are
they different?
Meiosis
Using two successive
divisions to reduce the
number of
chromosomes by half
and create gametes.
Homologous
chromosomes: a
pair of
chromosomes with
the same genes (but
may have different
alleles); one from
each parent.
Mitosis vs. Meiosis
Mitosis
Meiosis
# of divisions
1
2
# of daughter cells produced
2
4
# chromosomes in parent cell
46 (diploid)
46 (diploid)
# chromosomes in daughter cell
46 (diploid) 23 (haploid)
Type of cells produced
Somatic
(body) cells
Gametes
+*
(sex cells)