Cell Division
Mitosis
Meiosis
Growth
is a permanent increase in size accompanied by cell division and differentiation to form tissues & organs
Mitosis take places during growth
is a form of nuclear divisions that produces daughter nuclei containing the same number of chromosomes as parent nucleus. (genetically similar)
Cell Cycle
I nterphase
M itosis
C ytokinesis
the non-dividing stage of a cell
cells still carry out cell activities like absorbing nutrients
Before each cell divides, chromatin threads replicate
Two chromatin thread attached to the same centromere so they are called 'sister chromtids'
Furrows / cleavage appear in the cytoplasm between the two nuclei
The furrows deepen and 2 identical daughter cells are produced
is a form of nuclear division that produces daughter nuclei containing half the number of chromosomes s the parent nucleus
TWO nuclear divisions occur so there are 2 divisions in meiosis : meiosis I and meiosis II
meiosis can be summarised by I M C M C
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However, for meiosis at Prophase I, crossing over occurs.
Homologous chromosomes (a pair of chromosomes, one from the father and the other from the mother) pair along their whole length
Chromatids cross and twist around one another and the point where they cross is called a chiasma.
Importance of mitosis
Mitosis enables growth of an organism
Mitosis is needed for the repair & growth of worn-out parts
Mitosis allows asexual reproduction to occur.
Importance of meiosis
Meiosis produces haploid gametes. Gametes are reproductive cells that contain haploid number of chromosomes.
Meiosis results in variation in the gametes produced
Variation occurs because of 1. crossing over 2. independent assortment of chromosomes 3. random fertilisation
Variations increase the chances of survival of the species during changes in the environment
Differences