1.6 Genetic information copied and passed to daughter cells

• What are chromosomes made of?

  DNA and histone proteins
• What is chromatin?

  Unwound chromosomes in non-dividing cells
• What happens to DNA before cell division?

  It replicates into two identical molecules
• What is the area where two identical DNA molecules are joined called?

  Centromere
• What occurs at the beginning of cell division?

  Chromatin condenses and becomes visible
• What are the two identical parts of a chromosome called?

  Chromatids
• What are sister chromatids?

  Identical chromatids joined by the centromere
• What are homologous pairs of chromosomes?

  Chromosomes in pairs from each parent
• Why are homologous chromosomes termed homologous?

  They are the same size, shape, and gene order
• What can be said about the alleles in homologous pairs?

  They can be the same or different
• How do homologous chromosomes differ from sister chromatids?

  Homologous chromosomes are not identical; sister chromatids are
• Cells where the chromosomes are paired are termed diploid, these are body or somatic cells.

  Cells where the chromosomes are unpaired are termed haploid, these are gametes. Some organisms have body cells that are haploid.

  Diploid cells can divide by mitosis or meiosis. Haploid cells can only divide by mitosis.

  
• The cell cycle consists of several stages, as shown on the right.

  G1, S and G2 phases are collectively called interphase.

  The S phase is where DNA replication takes place and only happens if the cell is going to proceed to mitosis or meiosis. Cells that are carrying out their functions are in G1 phase for their lifespan.

  Mitosis describes when chromosomes move into new nuclei.

  Cytokinesis is the division of cytoplasm to form two new cells, each with a nucleus.

  In interphase, the cell is:

  • synthesising ATP
  • making new organelles
  • carrying out protein synthesis
  • increasing in size
  • replicating DNA.

  
• What does phase A represent in the cell cycle?

  Interphase G1
• What happens to the DNA content per cell in phase B?

  It doubles due to DNA replication
• Why does the DNA content double in phase B?

  Because DNA has replicated in the S phase
• What occurs during phase C of the cell cycle?

  The cell undergoes mitosis
• What happens to the DNA content during mitosis in phase C?

  It remains constant
• What processes occur to chromosomes during phase C?

  They condense, align, and are pulled to poles
• What happens to the DNA content in phase D?

  It drops by half
• What process takes place during phase D?

  Cytokinesis
• What is the result of cytokinesis in phase D?

  Each new nucleus is in a new cell
• What are the four stages of mitosis?

  Prophase, metaphase, anaphase, telophase
• What happens to chromosomes during prophase?

  They condense and become visible as sister chromatids
• What joins sister chromatids together?

  Centromere
• What is the role of centrioles in prophase?

  They migrate to opposite sides of the cell
• What begins to form in animal cells during prophase?

  The spindle made by the centrioles
• What happens to the nuclear membrane during prophase?

  It disintegrates
• What occurs to chromosomes during metaphase?

  They migrate to the equator and attach to spindle fibres
• What completes during metaphase?

  The spindle
• How do chromosomes attach to spindle fibres in metaphase?

  By the centromere
• What happens during anaphase?

  Spindle fibres shorten, pulling chromatids to poles
• What divides during anaphase?

  The centromere
• What are chromatids called after anaphase?

  Chromosomes
• What occurs during telophase?

  Chromosomes reach poles and uncoil
• What happens to spindle fibres during telophase?

  They break down
• What is the significance of mitosis?

  Mitosis is essential for growth and repair
• What forms around each set of chromosomes in telophase?

  New nuclear membranes
• How does mitosis differ in plant and animal cells?

  Plant cells lack centrioles; animal cells have them
• What happens to the spindle during telophase in animal cells?

  The spindle degenerates at telophase