cell division

• cell continuity means that all cells develop from pre-existing cells
• what are chromosomes?

  coiled threads of DNA and protein that become visible in the nucleus at cell division
• how many chromosomes do humans have?

  46
• what is a gene?

  short section of DNA that contains the instructions for the formation of protein
• a haploid cell has 1 set of chromosomes
• what is haploid is humans?

  sperm and egg cells are haploid in humans.
• diploid cells have 2 sets of chromosomes
• chromosomes are in pairs in a diploid cell called homologous pairs
• what is interphase?

  The phase of the cell cycle where the cell is not dividing
• 90% of a cells life is in interphase
• chromosomes duplicate in interphases to make identical copies of themselves
• mitosis is a form of cell division in which 1 nucleus divides to form 2 nuclei, each containing the same number of chromosomes with identical genes
• where does mitosis take place?

  somatic cells
• what happens in prophase?

  chromosomes become visible as double stranded structures, spindle fibres form, nucleolus disappears and the nuclear membrane breaks down
• what happens in metaphase?

  The nuclear membrane completely breaks down, The chromosomes line up across the middle of the equator.
• what happens during anaphase?

  The spindle fibres contract at anaphase, chromosomes are pulled apart
• what happens during telophase?

  The spindle fibres break down, The nucleolus begins to reform. chromosomes elongate to form chromatin