Science

• Chromosome


  Self-replicating genetic material that directs the activities and functions of cells
• DNA


  • Genetic material located inside a chromosome in the nucleus of the cell
  • Helical structure consisting of two strands
  • Organized and packaged by proteins or histones into different levels of chromosome packaging
• Chromosome packaging


  1. DNA helix forms nucleosomes

  2. Nucleosomes form 30-nanometer chromatin fiber

  3. Chromatin fiber forms supercoiled loops

  4. Supercoiled loops form mitotic chromosome
• The number of chromosomes in a cell is a characteristic of the species
• Chromosome number of selected organisms

  • Drosophila melanogaster (fruit fly): 8
  • Canis familiaris (dog): 78
  • Homo sapiens (human): 46
  • Oryza sativa (rice): 24
  • Zea mays (corn): 20
• Cell cycle


  1. Interphase

  2. Mitosis
• Interphase


  Interval between two cell divisions where the cell grows, replicates DNA, and prepares for mitosis
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• Mitosis


  • Produces two genetically identical daughter cells
  • Involves nuclear division (karyokinesis) and cytoplasmic division (cytokinesis)
• Cytokinesis in animal cells

  Cleavage furrows form and deepen to separate the two daughter cells
• Cytokinesis in plant cells

  Cell plate forms between the two new nuclei
• Meiosis


  Cell division process that produces haploid gametes (sex cells)
• Somatic cells have diploid chromosome number, gametes have haploid chromosome number
• Meiosis reduces the chromosome number by half to maintain the diploid chromosome number after fertilization
• Meiosis


  Process that decreases the chromosome number by half
• Meiosis must take place to produce sperm and egg
• Zygote


  New cell formed when a sperm unites with an egg, containing the normal diploid number of chromosomes (46)
• Without meiosis, the union of two gametes during fertilization would result in offspring with twice the normal number of chromosomes
• Meiosis


  1. Meiosis I

  2. Meiosis II
• Meiosis I


  • Reduction division (diploid to haploid)
  • Two daughter cells produced, each with haploid number of chromosomes
• Meiosis I


  1. Prophase I

  2. Metaphase I

  3. Anaphase I

  4. Telophase I
• Prophase I


  • Leptotene
  • Zygotene
  • Pachytene
  • Diplotene
  • Diakinesis
• Synapsis


  Pairing of homologous chromosomes
• Crossing over


  Exchange of genetic material between sister chromatids of homologous chromosomes
• Chiasma


  Point where homologous chromosomes touch and exchange genetic material
• Meiosis II


  1. Prophase II

  2. Metaphase II

  3. Anaphase II

  4. Telophase II
• Meiosis II results in four haploid daughter cells
• Differences between Mitosis and Meiosis


  • Location
  • Chromosome number of parent cell
  • Chromosome number of daughter cell
  • Number of daughter cells produced
  • Number of nuclear divisions
  • Steps required to complete the cell division phase
  • Occurrence of synapsis
  • Occurrence of crossing over
  • Presence of chiasma
  • Kind of reproduction associated with
• Roles of Mitosis and Meiosis

  • Mitosis: Somatic cell production
  • Mitosis: Asexual reproduction
  • Mitosis: Genetic stability
  • Mitosis: Repair of damaged cells/tissues
  • Meiosis: Gamete production
  • Meiosis: Sexual reproduction
  • Meiosis: Genetic diversity
  • Meiosis: Repair of genetic defects
• the first word in the organism's binomial name is the genus
• Genetics


  A branch of science that deals with the study of heredity and variation
• Heredity


  The transfer of traits from parent to offspring through the union of gametes
• Gregor Johann Mendel


  • Augustinian monk, Czech Republic
  • Foundation of modern genetics
  • Studied segregation of traits in the garden pea (Pisum sativum) beginning in 1854
  • Published his theory of inheritance in 1865. "Experiments in Plant Hybridization"
  • Mendel was "rediscovered" in 1902
• Gregor Johann Mendel


  He formulated the Law of Dominance, Law of Segregation and Law of Independent Assortment
• Gregor Johann Mendel


  Father of Genetics
• Law of Dominance


  The dominant trait dominates or prevents the expression of the recessive trait
• Dominant Gene


  The trait being expressed
• Recessive Gene


  The trait being masked or hidden
• Law of Segregation


  The pair of genes segregate or separate from each other during gamete formation
• Law of Independent Assortment

  The distribution or assortment of one pair of factors is independent of the distribution of the other pair