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CHAPTER 2
MITOSIS AND MEIOSIS
Honors Genetics
Lemon Bay High School
Chromosomes vs. Chromatids
Each sister
chromatid was
inherited from
one parent and
contains
identical gene
sites (loci)
along their
lengths.
QUESTION
• With regard to the
homologous chromosomes
pictured at right:
• How many sister chromatids
are present?
• How many chromosomes are
present?
• How many PAIRS of
homologous chromosomes are
present?
QUESTION
• With regard to the
homologous chromosomes
pictured at right:
• How many sister chromatids
are present?
• 16
• How many chromosomes are
present?
• 8
• How many PAIRS of
homologous chromosomes are
present?
• 4
2.3: Purpose of Mitosis
• Partitions chromosomes into dividing cells.
• Necessary for both Asexual and Sexual reproducing
organisms.
• Asexual
• Unicellular organisms such as protozoans and some fungi
• Basis for the production of new organisms.
• Sexual
• Multicellular organisms begin life as a single fertilized egg = ZYGOTE.
• Mitotic activity that follows is the foundation for growth and development of the
organism.
• Occurs in two phases
• Karyokinesis
• Interphase, replication of DNA, growth, cell “work”, mitosis
• Cytokinesis
• Division of cytoplasm and organelles into two new cells.
Cell Cycle/Cell Clock
Time
spent
from end
of one
cycle
(cell life)
to the
start of
next
cycle
(cell life).
• G1
• Birth of new cell
• Metabolic activity
• Cell growth
• Cell differentiation
• G0 = Quiescence
• Metabolic activity
• Non-proliferative = will not
undergo mitosis
• S = Synthesis
• Replication of DNA
• G2
• Metabolic activity
• Cell growth
• Cell differentiation
• Volume of cell has roughly
doubled
M = Mitosis
• No Metabolic activity
• No cell growth
• Occurs in 4 steps
• Prophase
• Metaphase
• Anaphase
• Telophase
What determines Quiescence?
The Type of Cell
• Labile
• Stabile
• Permanent
Prophase
• Over one half of mitosis is spent in
Prophase
• Centriole
• Migrates to opposite poles of the cell
• Forms spindle fibers from centriole to centriole
• Breakdown of nuclear envelope
• Chromatin condenses to form
chromosomes made of chromatids (the
duplication of a single chromosome).
Pro-Metaphase
• Chromosome movement toward the equator
of the cell.
• Kinetochore is the joining of the spindle fiber
to the centromere. Improper connection can
result in devastating results for the resulting
cell.
Metaphase
• Chromosomes are aligned along the midline
of the cell, what is called the metaphase plate.
Anaphase
• Critical phase of chromosome distribution
• The shortest phase of mitosis
• Sister chromatids of each chromosome disjoin
and migrate to opposite poles.
• For complete disjunction, each centromere
MUST split in 2.
• Molecular motors PULL the new daughter
chromosomes to opposite pulls with help of
the spindle fibers.
Telophase and Cytokinesis
• Final stage of Mitosis
• As cells pull apart cell membrane and
cytoplasmic structures, a cell furrow appears.
This is where the cell pinches to begin
formation of 2 new cells
• New nuclear membranes begin to form around
the daughter chromosomes.
• Spindle fibers disappear
• Cell enters Interphase.
Text reading
• Section 2.3 Mitosis
• Pay special attention to Cell-Cycle Regulation
and Checkpoints.
• Class Text page 22 - 26
• Online Text page 23 - 28