mitosis cytokinesis first phase of growth, the cell grows and develops, and additional organelles...
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Mitosis
Cytokinesis
First phase of growth, the cell grows and develops, and additional organelles are synthesised, the nucleus directs protein synthesis.
Synthesis of DNA, the DNA of the chromosomes is replicated
Second phase of growth, further synthesis of organelles occurs, chromosomes start condensing
Nuclear division
Cytoplasmic division
InterphaseCentriole
Chromosome
Nucleolus
Cell synthesizes more cytoplasm and organelles, chromosomes replicate, cell builds up large store of energy
is long and thin, cannot be seen under the light microscope
MITOSIS
ProphaseChromosome
Shortens and condenses, becomes visible under the light microscope
Nucleolus Gradually disappears
Prophase
Chromatid
Centromere
Centrioles move towards opposite poles of the cell
Prophase
Sister chromatids
Nuclear membraneBegins to break down
CentrioleMicrotubules extend from here towards the equator of the cell to form the spindle
MetaphaseSpindle fibre
Spindle equator
Spindle pole
Centromere becomes attached to a spindle fibre and moves to the equatorial plane
Chromosomes line up at the equator of the spindle
Anaphase
Centromere divides and the daughter chromosmes move to opposite poles with centromere leading
Daughter chromosome
Telophase
Nuclear membraneSurrounds daughter chromosomes
Nucleolusreforms
Chromosomes uncoil and gradually become invisible under light microscope
Division of the cytoplasm
Animal cell
Cell membrane invaginates at the mid point of the cell dividing the cell into two, cells are diploid (2N) and are identical to each other
Plant cellTiny vesicles containing cell wall materials coalesce to form the cell plate
Cell plate extends outward to the cell wall and separates cell into two
MEIOSIS
Meiosis I
Prophase I
Bivalent
Pairing of homologous chromosomes
maternal and paternal chromosomes come together and lie close to each other
Prophase I
Sister chromatids separate and become visible, they are held together by the centromere
Prophase I
Crossing over occurs between chromatids of homologous chromosomes
Chiasma
Metaphase ICentromere becomes attached to individual spindle fibre
Chromosomes lie at the equator of the spindle with members of each homologous pair facing opposite poles
Anaphase I
Members of each homologous pair move towards opposite poles
Telophase INuclear membrane reforms around the chromosomes
Cell divides into two
Prophase II
Nuclear membrane disappearing
Metaphase II
Chromosomes attached to spindle fibres by their centromere, line up at the equator of the spindle
Anaphase II
Centromeres divide and separate, pulling the sister chromatids to the opposite poles
Telophase II
Nuclear membrane forms around the chromosomes
Interphase
Four haploid (N) daughter cells are produced
Comparison between mitosis and meiosis
Mitosis MeiosisPairing of
homologous chromosomes
No Yes
Crossing over No Yes
Anaphase Sister chromatids separate during anaphase
Homologous chromosomes separate during anaphase I, sister chromatids separate during anaphase II. Number of
divisions involved One Two
Daughter cells Two diploid (2N) daughter cells, they are identical
Four haploid (N) daughter cells, they are non-identicalOccurrence During growth,
asexual reproduction
Production of gametes for sexual reproduction
• Clegg C.J., Mackean D.G., Advanced Biology: principles and applications
• Enger/Ross, Concepts in Biology
CROSSING OVER - exchange of genetic material between non-sister chromatids
Non-sister chromatids overlap
Once overlap, they break
Join with broken fragments of non-sister chromatid i.e. exchange of genetic material occurs
Crossing over - ChiasmaChiasmata have two functions: (1) hold the homologous chromosomes together as they move to the equator of the spindle (2) allow exchange of genetic materials between homologous chromosomes giving rise to genetic variations in the offspring