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Summary Chromosomes and Meiosis
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IEB Finals Chromosomes and Meiosis Notes. These notes contain the information needed as required by IEB study guide. It includes definitions, explanations and diagrams.
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Chromosomes and Meiosis:Nucleus: Membrane-bounded organelle, in eukaryotic cells, that contains
the genetic material
Unduplicated Chromosome: Single linear strands
Duplicated Chromosome: Contain two identical copies
Chromatids: Two identical copies of chromosome
Homologous Pair: Chromosome pairs of approximately the same length,
centromere position and staining pattern, for genes with same
corresponding loci (for each paternal, there is a matching maternal
chromosome)
Paternal and Maternal Chromosomes: Individual homologous
chromosome inherited from either the mother or father
Centromere: Specialised DNA sequence of a chromosome that links a
pair of sister chromatids
Centrosome: Organelle where cell microtubules are mainly organised, it
also regulates the cell division cycle
Diploid: Containing two complete sets of chromosomes, one from each
parent (46 chromosomes; 23 pairs)
Haploid: Having one complete set of chromosomes (23 chromosomes)
Karyotype: An organised profile of an organisms chromosomes
Chromatin Network: Found in nuclei of cell
Chiasmata: The points of crossing over where the chromatids break
Synapsis: Process whereby the replicated homologous pairs of
chromosomes come together to form bivalents
Recombinant chromatids: Genes from maternal chromatid that changed
place with genes from a paternal chromatid
Parental chromatids: Outer unchanged chromatids
, The Process of Meiosis:
The DNA of the parent cells is replicated in interphase before meiosis and
this replication is followed by two divisions:
• Meiosis 1: a reduction division which results in two cells being
formed each with half the number of chromosomes of the parent
cells (haploid nr)
• Meiosis 2: a copying division which involves the two haploid cells
formed, each dividing again by mitosis to form 4 haploid cells
Meiosis 1 - a Reduction Division:
Early Prophase 1:
Chromosomes become short and fat and are
visible as two chromatids joined by a centromere
* stage that crossing over takes place
Late Prophase 1:
1. Chromosomes of homologous pairs lie
1
along side one another, forming a
bivalent
2
2. The centrioles move to opposite
3
poles
nuclear membrane
3. A spindle, made up of protein breaks down
threads, develops across the cell from
the two centrioles
Metaphase 1:
The bivalents move to the middle of the cell and line
up on the equator
The centromeres become attached to the spindle
threads
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