Cell Division

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Cell Division contracts, the chromatids are slightly pulled remain jointed along points called
away from each other. Chiasmata.
Cell Division plays an important role in all Anaphase: the centromeres spilt apart and The crossing-over of chromosomes causes
organisms. the spindle fibres contract further. The genetic variation and is caused by the
There are two types of cell division, Mitosis chromatids are pulled towards the poles by swapping over of pieces of chromosomes.
(growth and repair) and Meiosis (games the centromere. Metaphase I: as in Mitosis, the
production). Telophase: the chromatids are referred to as chromosomes line up at the equator, but do
chromosomes at this stage. The spindle so in Random Distribution and than
A Karyotype: breaks down and the centrioles replicate. separate in Independent Assortment so
Chromosomes are found in pairs called The nucleoli and nuclear membrane reform. that different combinations are produced.
Homologous Pairs. Animal Cells- cytokinesis occurs. Plant Cells- This lining up and separation increases the
A full complement of chromosomes is cell plate forms between the cells for the new genetic combinations which increases
referred to as Haploid. cellulose cell wall to form. variation.
There are three types of variation caused by
The Cell Cycle: Importance of Mitosis: meiosis; Fusion of gametes causes
This is a continuous cycle that cells undergo Mitosis is important for growth, replacing genotype mixing, independent
but it is divided into four stages for easy dead cells and tissue repair. assortment of chromosomes and random
understanding. In asexual reproduction in plants, bacteria distribution and the crossing over of
Interphase- thinking and yeast mitosis is required to produce chromosomes.
Prophase- sort themselves out clone offspring which are genetically
Metaphase- line up identical to the parent. Comparison:
Anaphase- separate into cells The production of cells in an organism needs Meiosis Mitosis
Telophase- is 2 different cells to replicate chromosomes exactly. Therefore, Daughter cells are Daughter cells are
mitosis can produce genetically identical genetically different genetically identical
Mitosis: cells to provide GENETIC STABILITY to an Haploid number of Diploid number of
Interphase: known as the resting phase. organism. chromosomes chromosomes
Cell organelles double, DNA doubles, a lot of Crossing over No Crossing over
metabolism occurring so there is a lot of ATP Meiosis: Homologous pairs Homologous pairs
and the chromosomes are not visible as - occurs in gamete production only. form bivalents DO NOT FORM
chromatin, but is spread in the nucleus. - produced 4 haploid cells so that a diploid (Synapsis) PAIRS
Prophase: chromatin pairs condense and zygote can be formed at fertilisation. Two divisions 1 division only
can now be seen; the centrioles divide and - involves two divisions, Meiosis I followed by
move to the poles of the cell. The protein Meiosis II.
microtubules form from the centrioles and - Stages of division are the same for Mitosis
these form the spindles. At the end of this but occur twice in Meiosis, once in each
stage the nuclear membrane breaks down. division.
The nucleus disappears and the sister Prophase I: the chromosomes condense
chromatids can be seen in the cytoplasm. and are in their homologous pairs. When
Metaphase: chromosomes are arranged they pair up it is called Synapsis.
along the equator of the spindle and the Each pair of chromosomes is called a
chromosomes are attached by their bivalent, and when crossing-over occurs the
centromere to the spindle. When the spindle chromosomes repel each other slightly but


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