Skill: • Identification of phases of mitosis in cells viewed with a microscope or in a micrograph
Mitosis is the process of nuclear division, whereby duplicated DNA molecules are arranged into two separate nuclei Mitosis is
preceded by interphase and is divided into four distinct stages: prophase, metaphase, anaphase, telophase - The division of the cell in two (cytokinesis) occurs concurrently with the final stage of mitosis (telophase)
Before Mitosis
Interphase:
- DNA
is present as uncondensed chromatin (not visible under microscope)
- DNA is contained within a clearly defined nucleus
- Centrosomes and other organelles have been duplicated
- Cell is enlarged in preparation for division
Stages of Mitosis
Prophase:
- DNA supercoils and chromosomes condense (becoming visible under microscope)
- Chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)
- Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres
- The nuclear membrane breaks down and the nucleus dissolves
Metaphase: - Microtubule spindle fibres from both centrosomes
connect to the centromere of each chromosome
- Microtubule depolymerisation causes spindle fibres to shorten in length and contract
- This causes chromosomes to align along the centre of the cell (equatorial plane or metaphase plate)
Anaphase: - Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
- Once the chromatids separate, they are
each considered an individual chromosome in their own right
- The genetically identical chromosomes move to the opposite poles of the cell
Telophase: - Once the two chromosome sets arrive at the poles, spindle fibres dissolve
- Chromosomes decondense (no longer visible under light microscope)
- Nuclear membranes reform around each chromosome set
- Cytokinesis occurs
concurrently, splitting the cell into two
Overview of the Process of Mitosis Cells divide and reproduce in two ways, mitosis and meiosis. Mitosis results in two identical daughter cells, whereas meiosis results in four sex cells. Below we highlight the keys differences and similarities between the two types of cell division. DifferencesMitosis- Involves one
cell division
- Results in two daughter cells
- Results in
diploid daughter cells (chromosome number remains the same as parent cell)
- Daughter cells
are genetically identical
- Occurs in all organisms except viruses
- Creates all body cells (somatic) apart from the germ
cells (eggs and sperm)
- Prophase is much shorter
- No recombination/crossing over occurs in prophase.
- In metaphase individual chromosomes (pairs of chromatids) line up along the equator.
- During anaphase the sister chromatids are separated to opposite poles.
Meiosis- Diploid parent cell
- Consists of interphase, prophase, metaphase, anaphase and telophase
- In metaphase individual chromosomes (pairs of
chromatids) line up along the equator.
- During anaphase the sister chromatids are separated to opposite poles.
- Ends with cytokinesis.
SimilaritiesMitosis- Involves two successive cell divisions
- Results in four daughter cells
- Results in
haploid daughter cells (chromosome number is halved from the parent cell)
- Daughter cells are genetically different
- Occurs only in animals, plants and fungi
- Creates germ cells (eggs and sperm) only
- Prophase I takes much longer
- Involves
recombination/crossing over of chromosomes in prophase I
- In metaphase I pairs of chromosomes line up along the equator.
- During anaphase I the sister chromatids move together to the same pole.
- During anaphase II the sister chromatids are separated to opposite poles.
Meiosis- Diploid parent cell
- Consists of interphase, prophase, metaphase, anaphase and telophase (but twice!)
- In metaphase II individual
chromosomes (pairs of chromatids) line up along the equator.
- During anaphase II the sister chromatids are separated to opposite poles.
- Ends with cytokinesis.
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What phase do sister chromatids separate and move to opposite poles?
A central feature of mitosis is segregation of sister chromatids to opposite poles during anaphase.
In which stage do the chromatids get separated and move toward opposite ends of the cell a PB QC Rd S?
In anaphase, there is a shortening of the spindle microtubules. Each chromosome is pulled along by its centromere the two sister chromatids of each chromosome are pulled apart by the spindle and dragged by their kinetochores toward opposite poles of the cell.
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