Download Cellular Basis of Reproduction

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Reproduction is a characteristic of life.
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Reproduction of individuals depends on the
reproduction at the cellular layer
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From the cell theory, all cells arose from pre
existing cells
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Nucleus- control center of the cell
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Nucleus contains chromosomes which bear
the genes
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Nucleus carries “blueprint”
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Genes- unit of information passed from
generation to generation
-determine the characteristics of
each new organism and directs its many
activities
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when the cell divides, the nuclear information
must be transmitted in orderly fashion to the
new cells
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Bacteria reproduce asexually by binary
fission.
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A bacterium possesses a single, circular
chromosome which is replicated; and then
the replicates (chromosomes) are distributed
to two new cells formed by division of the
original cell.
Carina Perete DVM
Carina Perete DVM
Carina Perete DVM
The eukaryotic cell cycle has 5 main phases:
1. G1 (gap phase 1)
2. S (synthesis)
3. G2 (gap phase 2)
4. M (mitosis)
5. C (cytokinesis)
The length of a complete cell cycle varies
greatly among cell types.
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Interphase
 G1 growth phase; synthesis of organelles
 S synthesis of DNA (replication)
 G2 growth; synthesis of proteins essential to
cell division
 -each chromosome in the cell consists of two
identical sister chromatids
 Cell is preparing to divide
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Mitosis
 prophase
 metaphase
 anaphase
 telophase
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Carina Perete DVM

Mitosis
 provides cells for growth, cell replacement, and
asexual reproduction
 maintains chromosome number

Meiosis
 produces cells for sexual reproduction
 reduces chromosome number by half
Carina Perete DVM
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chromatin - the form taken by chromosomes
when a eukaryotic cell is not dividing
monad chromosome - unreplicated
chromosome (single chromosome)
dyad chromosome - replicated chromosome
(double chromosome)
chromatid - half of a dyad chromosome
centromere - structure by which chromatids
of a dyad chromosome are held together
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Carina Perete DVM
Carina Perete DVM
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Part of the cell cycle where the cell is actually
dividing

Nucleus and its contents divide and are
evenly distributed forming 2 daughter nuclei
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Prophase: dyad (replicated) chromosomes
resemble long threads (chromatin)

replicated centrioles move apart toward
opposite poles; (animal cell)
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nucleolus disappears; dyad chromosomes
condense (coil tightly);
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nuclear membrane disintegrates
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spindle fibers appear between centrioles;
dyad chromosomes migrate toward the
equator of the cell
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Carina Perete DVM
Prometaphase:
-chromosomes become attached to the spindle
apparatus by their kinetochores
-a second set of microtubules is formed from
the poles to each kinetochore
-microtubules begin to pull each chromosome
toward the center of the cell
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Carina Perete DVM
Carina Perete DVM
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2. Metaphase: dyad chromosomes line up
along the equator of the cell
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Carina Perete DVM
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3. Anaphase: dyad chromosomes separate
forming monad chromosomes;
monad
chromosomes move toward opposite poles
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Carina Perete DVM
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4. Telophase: monad chromosomes cluster
at poles; cytokinesis occurs gradually; nuclear
membrane forms; nucleolus reappears;
chromosomes uncoil; cytokinesis is
completed; two daughters cells are formed
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Carina Perete DVM
Carina Perete DVM
Cytokinesis – cleavage of the cell into equal
halves
-in animal cells – constriction of actin filaments
produces a cleavage furrow
-in plant cells – plasma membrane forms a cell
plate between the nuclei
-in fungi and some protists – mitosis occurs
within the nucleus; division of the nucleus
occurs with cytokinesis
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Carina Perete DVM
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have the same number of chromosomes as
each other and as the original cell from which
they were formed
e.g. Mitosis in a cell which possesses 4
chromosomes will result in the formation of
two daughter cells each having 4
chromosomes.
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
Mitosis
 provides cells for growth, cell replacement, and
asexual reproduction
 maintains chromosome number

Meiosis
 produces cells for sexual reproduction
 reduces chromosome number by half
Carina Perete DVM
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preceded by interphase which includes
chromosome replication
two meiotic divisions
four daughter cells produced
daughter cells contain half the number of
chromosomes as the original cell
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monad chromosome - unreplicated
chromosome
dyad chromosome - chromosome composed
of two chromatids (replicates)
homologous - similar in size and shape
synapsis - pairing of homologous
chromosomes
crossover - exchange of segments between
chromatids of homologous chromosomes
Carina Perete DVM
Carina Perete DVM
Chromosomes are replicated
during S-phase of interphase. As
a result, monad chromosomes
become dyad chromosomes.
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Prophase I: homologous chromosomes of
diploid cell synapse; homologous pairs
migrate toward equator of cell; crossover
may occur during synapsis
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Metaphase I: dyad pairs of homologous
chromosomes align at the equator of the cell
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Anaphase I: homologous chromosomes
move apart toward opposite poles
Telophase 1: chromosomes cluster at poles
of cell; cytokinesis occurs forming two
haploid daughter cells each containing one
member of each homologous pair thus
reducing chromosome by half
Carina Perete DVM
Carina Perete DVM
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Prophase II: dyad chromosomes move
toward the equator of each cell (2)
Metaphase II: dyad chromosomes align at
equator of cell
Anaphase II: dyad chromosomes separate
forming monad chromosomes (chromatids
separate); monads migrate toward opposite
poles of each cell
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Telophase II: cytokinesis occurs at right
angles to the first plane of division in each cell
(2); four daughter cells are formed each
having half the number of chromosomes as
the original cell
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meiosis in males – spermatogenesis
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meiosis in females - oogenesis
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4 mature sperm cells produced from meiosis
in a single spermatocyte
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one mature ovum (egg cell) and 3 polar bodies
formed from meiosis in a single oocyte
 human female embryo - oocytes formed by
mitosis and then complete prophase I of meiosis
by time of birth
 puberty - one oocyte in alternating ovaries
resumes meiosis under the influence of
hormones; at ovulation the oocyte is at
metaphase II
 oogenesis will be completed in the event of
fertilization
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Mitosis
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synapsis does not occur
one division occurs
two daughter cells are formed
chromosome number is maintained
Meiosis
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synapsis occurs during Prophase I
two divisions occur
four daughter cells are formed
chromosome number is reduced by half
Carina Perete DVM
•
•
Apoptosis is programmed cell death and involves a
sequence of cellular events involving:
• fragmenting of the nucleus,
• blistering of the plasma membrane, and
• engulfing of cell fragments by macrophages and/or
neighboring cells.
Apoptosis and cell division are balancing processes that
maintain the normal level of somatic (body) cells.
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•
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Cells normally hold caspases in check with
inhibitors.
Caspases are released by internal or external
signals.
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•
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Cell death is a normal and necessary part of
development: frogs, for example, must
destroy tail tissue they used as tadpoles, and
the human embryo must eliminate webbing
found between fingers and toes.
Death by apoptosis prevents a tumor from
developing.
Carina Perete DVM
Carina Perete DVM
Carina Perete DVM
1.
2.
3.
4.
5.
In what stage of your cell cycle does your
DNA replicate?
How many cells are produced in binary
fission of your bacterial cell?
What stage of your cell cycle is responsible
for active dividing of your cell?
What type of cellular reproduction produces
gametes for sexual reproduction?
What is the term for programmed cell
death?
Carina Perete DVM