Download Cellular Reproduction

Mitosis & Meiosis
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Chromatin – Thin, uncoiled strands of DNA &
proteins (histones)
Chromosomes – Rod-shaped structures
composed of coiled strands of DNA &
proteins.
Chromosomes are made up of two sister
chromatids held together at a central point
called a centromere.
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Chromosomes appear in pairs in all sexually
reproducing organisms.
◦ Called homologous chromosomes
◦ Same shape & same size
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Diploid number (2N) – A cell containing both
chromosomes of a homologous pair.
Haploid number (1N) – A cell containing one
chromosome of a homologous pair.
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SOMATIC CELL REPRODUCTION
◦ Somatic cells are body cells
◦ Germ cells are reproductive/sex cells
(gametes)
◦ Mitosis creates two daughter cells that are
exact replicas of the original cell
◦ Size causes a cell to divide
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G1 Period – Cell growth
S Period – DNA
Replication
G2 Period – Rapid cell
growth
Mitosis – Cell division
Cytokinesis –
Cytoplasmic division
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Comprised of the G1, S, & G2 periods.
A period of preparation for mitosis.
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Period of nuclear division
◦ Prophase
◦ Metaphase
◦ Anaphase
◦ Telophase
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Chromatin coils to form chromosomes.
Nucleolus & nuclear membrane disappear.
Spindle fibers begin to develop.
◦ Kinetochore fibers (pole to chromosomes);
◦ Polar fibers (pole to pole)
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Formation of asters.
Asters: Protein fibers that radiate from each pole.
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Chromosomes move to
the equator/center of
the cell.
Metaphase plate
formation
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Centromeres of each pair of
chromatids divide.
Chromatids separate & move
to opposite poles.
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Centrioles & spindle fibers
disappear
Chromatids unwind to form
chromatin
Nuclear membrane &
nucleolus reappear
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The division of the cytoplasm
ANIMAL CELL – cleavage furrow
PLANT CELL – cell plate formation
Cell Plate
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Process of nuclear division that reduces
chromosome number in half.
Used to create germ cells (gametes)
Two divisions
◦ Meiosis I
◦ Meiosis II
Crossing Over
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Prophase I
◦ Nuclear membrane/nucleolus disappear
◦ Chromosomes form from chromatin
◦ Homologous chromosomes line up together (tetrads)
◦ Crossing over occurs (Genetic Recombination)
◦ Spindle fibers form.
Metaphase I
◦ Homologous chromosomes move to equator.
Anaphase I
◦ Homologous chromosomes separate & move to poles.
Telophase I
◦ Cytoplasm divides (forms 2 daughter cells)
◦ Nuclear membrane & nucleolus reappear
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Most like Mitosis
Prophase II
◦ Nuclear Membrane & nucleolus disappear
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Metaphase II
◦ Chromosomes line up on equator
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Anaphase II
◦ Chromatids separate
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Telophase II
◦ Nuclear membrane & nucleolus reappear
◦ Chromosomes uncoil
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Spermatogenesis
◦ Occurs in males.
◦ Four sperm cells are
formed.
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Oogenesis
◦ Occurs in females.
◦ I egg (ovum)
formed.
◦ 3 polar bodies
formed, but
eventually
disintegrate.
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Not all cells move through the cell cycle at
the same rate.
◦ Nerve cells don’t divide at all once developed &
cells of skin grow & divide rapidly.
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Controls on cell growth can be turned on &
off.
Cyclins: Proteins that regulate the cell cycle
in eukaryotic cells.
Cancer: Cells fail to respond to signals that
regulate the cell growth.