SCIENCE 8

• Heredity


  Passing of traits from parents to children
• Trait


  Noticeable feature or quality in a person, passed on from generation to generation, showing similarities and differences
• Genetics


  Comes from the word gen, genetikas meaning generative and genesis meaning beginning
• Gene


  Basic unit of genetic information, determines the inherited characters

  
• Genome


  Collection of genetic information
• Chromosomes


  Storage units of genes
• DNA


  Nucleic acid that contains the genetic instructions
• Cell division


  • Growth and repair
• Some cells once fully formed do not undergo cell division such as nerve cells and muscle cells
• Rudolf Virchow


  Proposed the cell theory
• Cell Theory


  • Cells arise only from pre-existing cells
  • No new cells will be formed without pre-existing cells and no new organisms will be formed without a pre-existing organism
  • All cells undergo cell division
• Cellular reproduction

  • Asexual reproduction (genetic copies of parent)
  • Sexual reproduction (variety of offspring)
• Cellular reproduction in unicellular organisms (prokaryotic cell)

  1. Bacterial cells divide by binary fission (split into two)

  2. Replication of cytoplasm, cell membrane, DNA, and ribosomes

  3. New daughter cells are identical in content

  
• Cellular reproduction in multicellular organisms (eukaryotic cell)

  Rapid and successive rounds of cellular reproduction in human embryos to form vital organs and body parts in 9 months
• Stages of cellular reproduction

  • Cellular growth and maturation
  • Cell division
• Cell cycle

  • Checkpoints for surveillance and quality control of the genome to maintain genomic integrity
  • Checkpoint failure causes mutations and genomic arrangements resulting in genetic instability
• Interphase


  1. Cell is carrying out its normal life activities

  2. Chromosomes become duplicated

  
• Early Prophase

  1. Nuclear envelope begins to disappear

  2. Nucleolus disappears

  3. Long fibers of chromatin become evident and begin to condense as visible chromosomes

  
• Late Prophase

  1. Chromosomes continue to shorten and thicken

  2. Spindle forms between centrioles which have moved to the poles of the cell

  3. Kinetochores begin attaching to microtubules

  
• Metaphase


  Spindle fibers attach to the kinetochores of the chromosomes, which line up along the cell's midplane

  
• Anaphase


  Chromatids separate at the centromeres, and one group of chromosomes moves toward each pole

  
• Telophase


  1. Chromosomes have arrived at the poles, and the nuclear envelope begins to form

  2. Cytokinesis produces two daughter cells

  
• Daughter cells formed in interphase are genetically identical to the parent cell
• Meiosis


  Gametes (cells that contain only half of the chromosome number from the mother cell)

  
• Types of gametes in animals

  • Sperm cell
  • Egg cell
• Meiosis I (reductional division)


  Homologous chromosomes separate producing 2 haploid daughter cells

  
• Prophase I


  1. Homologous chromosomes pair to form bivalents

  2. Crossing over can occur leading to genetic recombination

  
• Metaphase I

  1. Bivalents align at the center of the cell or the metaphase plate

  2. Centrioles are located at each pole of the cell

  3. Spindle fibers produced by the centrioles attach in the centromere of the chromosome

  
• Anaphase I


  1. Bivalents separate going to opposite poles forming univalents

  2. Separation of bivalents is due to the action of spindle fibers

  3. Chromosome number is halved

  
• Telophase I

  1. Univalents move at the poles of the cell while the nuclear membrane reforms

  2. Univalents decondense to form thread like structures called chromatin

  3. Cytokinesis is almost finished

  4. 2 haploid daughter cells are produced

  
• Meiosis II (equational division)


  1. Functionally the same with mitosis

  2. DNA replication does not happen before entering Meiosis II

  3. Produces 4 haploid daughter cells

  
• Prophase II


  1. Univalents move at the poles of the cell while the nuclear membrane reforms

  2. Nuclear membrane disintegrates and chromatin condense to form chromosomes

  3. Synthesis of mitotic spindle by the centrioles

  4. Spindle fibers produced by the centrioles attach in the centromere of the chromosome

  
• Metaphase II


  1. Univalents align themselves at the center of the cells

  2. Centrioles are located at each pole of the cell

  3. Spindle fiber help migrate the chromosome towards the center of the cell

  
• Anaphase II


  1. Univalent separates at the centromere going to opposite poles forming individual sister chromatids

  2. Separation of univalents is due to the action of spindle fibers

  3. Cytokinesis starts

  
• Telophase II

  1. Sister chromatids moves at the poles of the cell while the nuclear membrane reforms

  2. Sister chromatids decondense to form thread like structures like chromatin

  3. Cytokinesis is almost finished

  4. 4 haploid daughter cells are produced

  
• Nucleus

  • Where cell division starts
  • Contains chromatin fibers (genetic materials of the cell in the form of long thin threads of DNA wrapped around histone proteins)
  • Fibers undergo compaction to form distinct and visible chromosomes
  • In humans, there are 25000 genes mostly contained in the 46 chromosomes
  • Each chromosome has a centromere, a region containing kinetochore, that serves as an attachment of the spindle fibers where the chromosomes are pulled to the opposite poles during cell division

  
• Centrioles


  Paired organelles found in the cytoplasm near the nucleus, duplicate themselves and each pair moves to the end poles of the cell to anchor themselves into spindle fibers

  
• Spindle Fibers


  Formed from the microtubules which are miniature tubes that support the cell
• Nuclear Membrane


  Disintegrates and the chromosomes are free to migrate towards opposite poles
• Cytokinesis

  • Cytoplasm of the cell and its organelles separate into 2 new daughter cells
  • In animals, a groove called the cleavage furrow forms pinching the parent cell in two daughter cells
  • In plants, a membranous cell plate splits the cell into two resulting to plate formation