Unit 3

• Eukaryotic chromosome


  Structure of a duplicated eukaryotic chromosome
• Diploid chromosome number


  Difference between diploid and haploid chromosome numbers
• Chromatin


  Difference between chromatin and a chromosome
• Cell cycle


  What happens during each phase of the cell cycle
• Cytokinesis


  The process of cytokinesis
• Cell cycle


  The cell cycle is under the control of genes and the behaviour of normal cells compared to cancer cells
• Patterns of inheritance


  Autosomal dominant, autosomal recessive, X-linked recessive
• Each human body cell has a full complement of DNA stored in 23 pairs of chromosomes
• Chromatin


  Composed of DNA and proteins, scattered throughout the nucleus, condenses to form chromosomes when the cell divides
• Sister chromatids


  Copies formed during S-phase of cell cycle
• Genotype


  An individual's complete genetic makeup
• Phenotype


  The characteristics that the genes express, whether they are physical, behavioral, or biochemical
• Allele


  A variant form of a gene
• Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome
• Cell cycle


  1. G1 phase: Cell increases in size, Cellular contents duplicated

  2. S phase: DNA replication, Each of the 46 chromosomes (23 pairs) is replicated by the cell

  3. G2 phase: Cell prepares for cell division

  4. M phase: Mitosis followed by Cytokinesis (cell separation), Formation of two identical daughter cells

  5. G0 phase: A phase where the cell has left the cycle and has stopped dividing
• Cytokinesis


  The final step of cell division - two daughter cells become physically separated
• Deregulation of cytokinesis has been linked to various diseases, including cancer, blood disorders, female infertility, oculocerebrorenal syndrome, and age-related macular degeneration
• Microtubules are depicted in blue, the actomyosin contractile ring and the midbody ring in red, and the endosomal sorting complex required for transport (ESCRT)-III spiral filaments in green (ESCRT = endosomal sorting complex required for transport)
• Restriction point (R)


  Located at G1 and is a key checkpoint - cells that pass through the R point will end up completing the entire cell cycle
• p53


  A tumour suppressor gene that stops the progression of the cell cycle
• Cyclins


  Control cell progression by activating cyclin-dependent kinase (CDK) enzymes
• Neoplasia is abnormal and excessive growth of cells
• A defect in p53 tumour suppressor gene > cannot detect and bind to cells with damaged DNA to either repair the damage or cause apoptosis > unchecked replication of cells > neoplasia
• Methotrexate is an antimetabolite of the antifolate type, inhibits dihydrofolate reductase (DHFR), an enzyme that participates in the tetrahydrofolate (a folic acid derivative) synthesis, Folic acid is needed for the de novo synthesis of the nucleoside thymidine - required for DNA synthesis, Methotrexate, therefore, inhibits the synthesis of DNA, RNA, thymidylates, and proteins
• Autosomal dominant


  Phenotype associated with a given version of a gene is observed when an individual has only one copy
• Autosomal recessive


  Phenotype associated with a given version of a gene is observed only when an individual has two copies
• Sex-linked or X-linked inheritance


  A number of medical conditions in humans are associated with genes on the X chromosome, including haemophilia, muscular dystrophy, oculocerebrorenal syndrome and some forms of colour blindness
• Amniocentesis is a procedure for obtaining foetal cells for genetic testing
• Meiosis


  Cell division that produces haploid gametes from diploid cells
• Mitosis


  Cell division that produces diploid daughter cells genetically identical to the parent cell
• Meiosis I


  1. Homologous approach

  2. Homologous pair

  3. Synapsis and crossover (chromatid fragments exchanged)

  4. Separation

  5. Split at centromere
• Meiosis II


  1. Separation

  2. Split at centromere
• Results of meiotic division

  • Crossover – redistributes genetic material
  • Random distribution of homologous chromosomes to daughter cells
  • Haploid germ cell (gametes)
  • Diploid number restored upon fertilization
• Chromosomal abnormalities


  • Numerical – nondisjunction (separation fails)
  • Trisomy (24 + 23) or Monosomy (22 + 23)
  • Structural – chromosome breakage
  • Environmental factors – drugs, radiation and viruses
• Parthenogenesis


  Natural form of asexual reproduction in which growth and development of embryos occur without fertilization
• Parthenogenesis


  • Common in reptiles
  • Typically not viable in mammals
• XY Sex Determination


  • Women typically have two X chromosomes (46,XX karyotype)
  • Men usually have one X chromosome and one Y chromosome (46,XY karyotype)
• Sex


  Biological - The anatomy of an individual's reproductive system, and secondary sex characteristics
• Gender


  • Social and cultural - Gender role = social roles based on the sex of the person
  • Gender identity = personal identification of one's own gender based on an internal awareness
• Dihydro-testosterone


  Hormone that drives the development of the sex organs in males at around 8 weeks in the womb