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Mitosis and Meiosis (Mitosis (Replication (Mitosis is preceded by a…
Mitosis and Meiosis
Mitosis
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Chromosomes replicated during S phases are divided so that, each daughter cell receives an exact copy
Replication
Mitosis is preceded by a process of DNA replication that converts each chromosome into two sister chromatids
- Vital for tissue formation and maintenance
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Four phases
Prophase, Mmetaphase,Anaphase,Telophase
Chromosomes
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Highly condensed in metaphase, gene expression is shut down
in interphase, chromatin extended to allow gene expression
DEFINITION
Structure in a cell on which genes are located, consisting of a highly compacted stretch of DNA with associated proteins
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Meiosis
Production of Haploid gametes, also pro provide the opportunity for genetic recombination
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Nucleosome, the basic level of DNA packaging
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Variable length stretch of free DNA separates adjacent nucleosomes and this is stabilised by one molecule of linker histone (String of beads)
Histomes are small, highly basic proteins, carry a positive charge and gives them an affinity for the negatively charged DNA
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Genome: Organisms complete set of DNA including all of its genes, Each genome contains all the information needed to build and maintain that organism
Metaphase: The stage of cell division when chromosomes are aligned at the centre of the cell prior to separation (Equatorial plane).+ Spindle forms, spindle fibres extend from the centrioles at the two poles of the mitotic figure, connecting the protein complex known as the kinetochore, located at the centromere.
Interphase: Stage of the cell cycle in between cell divisions. Compromises of three phases: G1,S and G2
Prophase: + Chromosomes begin to condense and the nuclear membrane breaks down + Centrosome duplicates and migrates to opposite sides of the cell +The centrosomes organise the production of microtubules that form the spindle fibres that constitute the mitotic spindle
Mitotic Spinde: Cytoskeletal structure of eukaryotic cells that forms during cell division to separate sister chromatids between daughter cells
Anaphase: Shortest stage of mitosis, Cohesin protein holding sister chromatids together is disrupted. Releasing chroaotids. + Spindle fibres contract and draw in Chromatids towards poles of the cell.
Telophase: Mitosis is completed and formation of two new daughter cells.+Spindle fibres disappear chromosomes start to unwind
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Gametogenesis: Production of gametes, occurs only in gonads. Uniqueness is assured by random segregation of maternal and paternal homologues. Recombination involves the exchange of DNA between paternal and maternal chromosomes
Chiasmata = the location of cross overs where the chromatids of homologous chromosomes have exchanged material in the late pachytene. - This cross over involves breakage of the DNA
Causes of Meiotic non-disjunction: increasing maternal age + Maternal hypothyriodism + after irradiation or viral infection + family tendancy