1.6 The cell cycle and cell division

• What is a chromosome?

  A long thin structure of DNA and protein
• What is a chromatid?

  One of the two identical copies of a chromosome
• What is a centromere?

  Point-like region where two chromatids join
• What happens to a chromosome after DNA replication?

  • Consists of two chromatids
  • Chromatids separate at anaphase
  • They are called chromosomes again after separation
• What are chromosomes made of?

  DNA and a protein called histone
• What is the structure of DNA in a chromosome?

  It is a double helix running the length
• What are sections of DNA along a chromosome called?

  Genes
• When do chromosomes become visible?

  When chromatin condenses prior to cell division
• What are sister chromatids?

  Two identical copies of a chromosome
• What joins sister chromatids together?

  The centromere
• What is the role of the DNA at the centromere?

  • Maintains structure of the chromosome
  • Contains a short sequence of bases that repeats
  • Does not carry genetic information
• How do chromosomes change after DNA replication?

  They consist of two sister chromatids
• What happens to chromatids during anaphase?

  They separate and are called chromosomes again
• Mitosis is the process by which one parent cell divides into two daughter cells.
• How many chromosomes do normal human body cells have?

  46 chromosomes
• How many chromosomes does a fruit fly have?

  8 chromosomes
• How many chromosomes does a potato have?

  48 chromosomes
• What are homologous pairs of chromosomes?

  Matching pairs from each parent
• How many pairs of homologous chromosomes do humans have?

  23 pairs
• What does it mean for an organism to be diploid?

  It has two complete sets of chromosomes
• What is the term for organisms with more than two complete sets of chromosomes?

  Polyploid
• What is the definition of haploid?

  • Having a single complete set of chromosomes.
• What are homologous chromosomes?

  • Same genes in the same sequence
  • May have different alleles
  • Separate during meiosis
• What is the definition of diploid?

  • Having two complete sets of chromosomes.
• What role do centromeres play during cell division?

  They attach chromosomes to spindle fibres
• What does mitosis produce?

  Two genetically identical daughter cells
• What are the main stages of the cell cycle?

  1. Interphase
  2. Mitosis
  3. Cytokinesis
• What is the S phase of interphase responsible for?

  DNA replication
• Why is interphase not a resting phase?

  Cells are metabolically very active
• What happens to DNA during interphase?

  DNA quantity doubles
• What is chromatin?

  Dispersed nuclear material
• What occurs during prophase of mitosis?

  Chromosomes condense and become visible
• What happens to the nuclear envelope during prophase?

  It disintegrates
• What is the role of centrioles during prophase?

  They move to opposite poles of the cell
• What happens to spindle fibres during telophase?

  They break down
• What is cytokinesis?

  Division of the cytoplasm
• How does cytokinesis occur in animal cells?

  By constriction around the equator
• How does cytokinesis occur in plant cells?

  By forming a cell plate
• What are the differences between mitosis in animal and plant cells?

  • Animal cells: Centrioles present, cleavage furrow develops
  • Plant cells: Centrioles absent, cell plate forms
• What is the longest phase of the cell cycle?

  Interphase