Anatomy and Physiology
Cellular Division
The Cell Cycle: Mitosis
The Cell Cycle
• The series of
changes that a
cell undergoes
from the time
it forms until
the time it
divides.
Interphase
Period between cell divisions when
a cell is carrying on its normal
functions and is preparing for
division.
• Stages of Interphase
• G1 - Growth phase - cells grow and develop,
rapid growth and protein synthesis.
• S - Synthesis phase - DNA replication
occurs.
• G2 - Growth phase - centrioles replicate,
cell prepares for cell division.
Mitosis
• Division of a
somatic cell to form
two genetically
identical nuclei.
• P.M.A.T
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
Mitosis
• Somatic Cells - body cells, chromosome
number is constant.
• Chromosomes exist in pairs.
– Ex. We have 23 pairs of chromosomes or 46
chromosomes.
• Called diploid or 2N (two homologous copies of
a chromosome)
• Each pair of chromosomes carries the genetic
information for the same trait - Homologous.
Chromosome Structure
• Sister Chromatids
– Duplicated
chromosome made in
S phase of
interphase.
• Centromere
– Holds sister
chromatids together.
4 Stages of Mitosis: Prophase
– Chromatin in the
–
–
–
–
nucleus condenses to
form visible
chromosomes.
Nuclear membrane
breaks down.
Nucleolus disappears.
Centrioles move to
opposite sides of the
cell.
Microtubules form
spindle fibers
attached to
centrioles.
4 Stages of Mitosis:
Metaphase
Chromosomes
align in the
center of the
cells and attach
to the spindle
fibers by their
centromeres.
4 Stages of Mitosis: Anaphase
• Centromeres
separate- sister
chromatids move to
opposite ends (poles)
of the cell.
• The individual sister
chromatids are now
call individual
chromosomes.
4 Stages of Mitosis:
Telophase
– Like prophase in
reverse.
– Chromosomes uncoil.
– Nuclear membrane
reforms around
chromosome set.
– Nucleoli become
visible inside nucleus
again.
– Spindle fibers break
down.
Cytokinesis: Cytoplasmic
Division
• Considered a
separate stage.
• Cell membrane
pinches in on
itself until 2
daughter cells
are formed.
Cytokinesis
Cell Differentiation
• The process by
which cells develop
different structures
and specialized
functions.
• Controlled by the
activation of certain
genes.
Stem Cells
• A precursor cell that can be triggered
by genes to become any type of cell.
Meiosis - Formation of Gametes
• Meiosis only occurs
during the
production of
gametes.
• After fertilization,
the diploid zygote
divides by mitosis
producing a
multicellular,
diploid organism.
Meiosis
• Meiosis reduces the chromosome number
from diploid to haploid.
• Occurs in two divisions, called meiosis I and
meiosis II.
• Divisions result in 4 daughter cells, each with
half the number of chromosomes as the
parent.
• Meiosis 1 separates the homologous
chromosomes (2 copies of each chromosome-1
from mom & 1 from dad) and Meiosis 2
separates sister chromatids.
Karyotype of a Female
Two Meiotic Divisions
Meiosis I
Meiosis II
Comparing Mitosis and Meiosis
Formation of Sperm vs.
Formation of Eggs