Cell division

• List the stages of the cell cycle in order and outline what happens at each stage

  G1 - Cellular contents excluding chromosomes are duplicated. Organelles duplicate, more cytoplasm, more membrane, energy storageS - Each of the chromosomes is duplicatedG2 - The cell 'double checks' the duplicated chromosomes for errors, making any needed repairs. Further increase in size and build up of energy store.Mitosis - Division of the nucleus (Prophase, Metaphase, Anaphase, Telophase)Cytokinesis - division of the cytoplasm(G0 - cell division stopped. Can undergo differentiation and specialisation)
• List the 3 stages of interphase in order and describe what happens at each stage

  G1 - grouwth of cell, duplication of organelles etc.S - Chromosomes duplicateG2 - Increase in size, Energy store, centrosomes replicate
• List the 2 stages of the mitotic phase and outline what happens at each stage

  Mitosis - nuclear division (PMAT)Cytokinesis - division of cytoplasm
• Describe the significance of G0 as a phase that cells enter when they leave the cell cycle.

  In G0, cells no longer divide to reproduce but can differentiate to become specialised for a specific function.
• Outline the role of checkpoints to control the cell cycle

  Checkpoints insure that each division is successful in producing two genetically identical daughter cells. They monitor and verify each stage is completed before the cell can move on to the next stage.
• State 3 examples of checkpoints in the cell cycle, where they occur and what is checked at each checkpoint

  G1 checkpoint: cell size, nutrients, growth factors, DNA damage (at end of G1)G2 checkpoint: cell size, DNA replication, DNA damage (at end of G2)Spindle assembly check point: chromosome attachment to spindles (at end of metaphase)
• Outline the link between cell-cycle regulation and cancer

  Cancer is caused by unregulated division of cells. This occurs when the proteins that regulate the cell cycle at the checkpoints do not function properly so division is uncontrolled and tumours form.
• Define the terms "mitosis", "chromosome", "chromatid", "sister chromatids", "centromere", "centrioles", "spindle fibres", "homologous pairs"

  Mitosis - nuclear division stage of the mitotic phase of the cell cycle. Results in two daughter cells each having the same number and kind of chromosomes as the parent nucleusChromosome - Structures of condensed and coiled DNA in the form of chromatin. Chromosomes become visible under a light microscope when the cell is preparing to divideChromatid - each of the two thread-like strands into which a chromosome divides longitudinally during cell division Sister chromatids - two identical copies of DNA (a chromosome) joined at a centromereCentromere - a region at which two chromatids are held togetherCentrioles - component of the cytoskeleton of most eukaryotic cells composed of microtubulesSpindle fibres - a network of filaments that collectively form a mitotic spindle (in mitosis) and meiotic spindle (in meiosis) and are responsible in moving and segregating the chromosomes during nuclear divisionHomologous pairs - matching pair of chromosomes, one inherited from each parent
• Describe how DNA is packaged in a chromosome

  Double-stranded DNA loops around histones, forming the nucleosome. DNA can be further packaged by forming coils of nucleosomes, called chromatin fibres. These fibres are condensed into chromosomes during mitosis, or the process of cell division.
• List the stages of mitosis in order


  Prophase, Metaphase, Anaphase, Telophase
• Draw, and annotate, a diagram for each stage of mitosis to show the events occurring at each stage

  Prophase - Duplicated chromosomes condense, Spindle fibres extending/being formed towards centromeres, Nuclear envelope fragmentingMetaphase - Chromosomes line up in centre of cell (equator of cell/mitotic plate) Spindle fibres attach to centromere of each chromosomeAnaphase - Each chromatid is separated into its sister chromatids. Spindle fibres shorten, pulling chromatids to each side of cellTelophase - Nuclear envelope reforming, chromosomes less condensed, unravelling.

  
• Explain the role of the centrioles and spindle fibres in mitosis

  Spindle fibres form from the centrioles. They attach to centromeres to separate the chromatids and draw them to each side of the cell to from the two new nuclei.
• Describe the process of cytokinesis in animal cells and plant cells (and compare the two)

  Animal cells: Cleavage furrow forms around the centre of the cell. Cytoskeleton draws membrane in until it is close enough to fuse to form two separate cellsPlant cells: Vesicles from golgi apparatus line up along centre of cell and fuse together forming the new cell membranes. New sections of wall then form along the new surface membranes.
• Describe the purpose of mitotic cell division and list 4 roles of mitotic cell division

  The purpose of mitosis is to create more identical cells.Growth, Repair, Replace, Asexual reproduction
• Define the terms "diploid", "haploid", "gamete", "zygote", "meiosis", and "reduction division"

  Diploid - A cell with 2n chromosomes (two copies of each chromosome, one from each parent)Haploid - A cell with n chromosomes (one copy of each chromosome) Gamete - A haploid germ cell - sperm of egg cell in animals. They fuse at fertilisation to produce a zygote.Zygote - The cell produced from the fertilisation of a haploid egg cell by a haploid sperm cellMeiosis - The form of nuclear division that results in the production of haploid nuclei from a diploid nucleusReduction division - Any form of nuclear division in which the chromosome number is reduced
• Explain the role of meiosis in life cycles

  Meiosis is needed for sexual reproduction. It halves the number of chromosomes so that the diploid number of chromosomes is restored at fertilisation. It produces genetic variation in offspring.
• State 2 ways in which meiosis produces variation

  Independent assortmentCrossing over
• Suggest the importance of the creation of different allele combinations in populations

  Genetic variation is important in populations. Makes them less vulnerable to disease or change in conditions as some will be more suited to new environment.
• Define the terms "homologous chromosomes", "bivalent", "crossing over", "chiasma" (chiasmata is plural), "recombinant chromatid" and "random independent assortment"

  Homologous chromosomes - matching pair of chromosomes, one inherited from each parentBivalent - The name for two homologous chromosomes that have paired up in prophase I of meiosis (The pair of chromosomes join by synapsis and an alternative name for the structure is a tetrad)Crossing over - The exchange of part of a chromosome between chromatids of homologous pairs. This occurs at chisamata.Chiasmata - Sections of DNA which became entangled during crossing over, break and rejoin during anaphase I of meiosis, sometimes resulting in an exchange of DNA between bivalent chromosomes, forming recombinant chromosomes and producing genetic variationRecombinant chromatid - chromatids with a combination of DNA from both homologous chromosomes, formed by crossing over and chiasmata in meiosisRandom independent assortment - The fact that which daughter cell a chromosome ends up in after Meiosis I or a chromatid ends up in after Meisosis II is random and independent of the fate of chromosomes from other homologous pairs.
• Draw, label and annotate a sequence of diagrams to show the stages of meiosis and what occurs at each stage

  Meiosis I - Chromosomes paired up - bivalents line up along centre of cellIt is the whole chromosomes that are pulled to each side of the cell still in duplicated form (2n to n)Meiosis II - Same mechanism as mitosis but with fewer chromosomes - chromatids are separated into each side of the cell.

  
• State the stages of meiosis in order

  Prophase I, Metaphase I, Anaphase I, Telophase I, Cytokinesis IProphase II, Metaphase II, Anaphase II, Telophase II, Citokinesis II
• Describe the process of crossing over and explain how it produces genetic variation

  Chromatids become entangled at the chiasmata, sections of DNA break off and are exchanged so that the chromatids no longer contain solely maternal or paternal DNA. This means that each of the 4 daughter cells are different and there are infinite possibilities for different combinations of DNA producing genetic variation in offspring.

  
• Describe the process of random independent assortment and explain how it produces genetic variation

  When bivalents line up in Meiosis I or chromosomes line up in Meiosis II, they have equal chance of lining up in a way that would make a particular chromosome go to one pole of the cell or the other. This means that each group of chromosomes at either pole will have some that originally came from the mother and some that came from the father.
• Explain (given the chromosome number of the species) how to calculate the total number of possible genetically different gametes that could be produced through independent assortment only

  The number of chromosomes squared