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Mitosis
What is Mitosis?
• Division of the nucleus plus
division of the cell itself
(cytokinesis)
• Produces two identical daughter
cells during prophase, metaphase,
anaphase, and telophase.
Stages of the cell cycle
• An ordered set of events,
culminating in cell growth and
division into two daughter cells.
• Non-dividing cells not considered
to be in the cell cycle.
Stages of the cell cycle
• INTERPHASE
– G1 stage = "GAP 1” cell growth
– S stage = "Synthesis”
• DNA replication
– G2 stage = "GAP 2” organelle production
• MITOSIS
– M phase = nucleus divides
• CYTOKINESIS
– cytoplasm divides  daughter cells
Regulation of the Cell Cycle
• Very complex
• Errors can lead to cancer.
–In cancer, regulation of the cell cycle
goes awry
–Normal cell growth & behavior is lost.
Ploidy
• Number of sets of chromosomes in
a cell
• Haploid (n)-- one set chromosomes
• Diploid (2n)-- two sets
chromosomes
• Most plant and animal adults are
diploid (2n)
• Eggs and sperm are haploid (n)
Chromosome Characteristics
• Diploid set for humans; 2n = 46
• Autosomes = body chromosomes
• Female-sex chromosomes =
homologous (XX)
• Male-sex chromosomes =
non-homologous (XY)
Interphase
• The cell is metabolizing, growing and
preparing for mitosis
Interphase
• Chromosomes are not clearly seen
• Nucleolus may be visible
• In animal cells ONLY, a pair of
centrioles may start moving into
position.
Prophase
• Chromatin begins to condense and
becomes visible.
• Nucleolus disappears.
• Centrioles begin
moving to opposite
ends of the cell
Prophase (con’t)
• Nuclear membrane dissolves
• Microtubules attach
and chromosomes
begin moving.
Metaphase
• Spindle fibers align the
chromosomes along metaphase
plate.
• Helps to ensure each
new nucleus will
receive one copy
of each chromosome.
Anaphase
• Paired chromosomes separate and
move to opposite sides
Telophase
• Chromatids arrive at opposite
poles
• Membranes re-form around
daughter nuclei.
• Chromosomes & spindles
disperse and are no
longer visible.
• Cytokinesis may begin
Cytokinesis: Animals
• Fiber ring of protein called actin around
center of cell contracts
• Pinches cell into two daughter cells
Plants
• In plant cells,
the rigid wall
requires that
a cell plate
be
synthesized
between the
two daughter
cells.
Asexual Reproduction
• Uses only mitosis
• Cells duplicate to form
2 exact copies (clones)
of each other
• Most primitive form of reproduction
–NO GENETIC VARIATION
• Used by higher organisms when
conditions are not favorable for
sexual reproduction
Types of Asexual Reprod.
• Binary fission
• Budding
• Fragmentation
• Regeneration
• Spore formation
• Parthenogenesis