Mitosis and Meiosis


Mitosis- is a type of division of the nucleus whereby a parent cell separates its chromosomes into _2_ identical daughter cells.


Steps of Mitosis

  • Interphase- The DNA is all stretched out and tangled like a big bowl of _spaghetti_ called chromatin. Next the cell duplicates its DNA. Each DNA molecule is called a chromatid and the pair of them are joined by structure called a centromere. _78_% of the time a cell is in this stage.
  • Prophase- The DNA has bunched up and is now _visible_! Centrioles migrate to the two sides of the cell. In late prophase, asters (protein tubes) from the centrioles (spindles if plants) attach to the _chromosomes_.
  • Metaphase- In metaphase the chromosomes line up in the _middle_ of the cell.
  • Anaphase- The asters pull the chromatids _apart_.
  • Telophase- The cell has now _divide_ but not split.
  • Cytokinesis- The cell membranes have pinched in and split the cell and its cytoplasm in _2_.


Mitosis scramble



Parent Cells
Daughter Cells
Homologous pair


Essential Questions:

1. What types of cells undergo mitosis?

2. What are the stages of mitosis and what occurs at each step?


Meiosis: a type of nuclear division that occurs only in special reproduction (_sex_) cells. Parent cells divide into four _haploid_ cells but they contain _1/2_ of the original number of chromosomes (monoploid).



Steps of Meiosis

Meiosis involves _2_ successive cell divisions which produce four monoploid cells.

  • Ist division: Similar to mitosis except the during prophase 1- the two chromosomes from the mother and two chromosomes from the father line up side by side called _sypapsis_. The 2 sets of chromosomes (sister chromatids) come together forming a _tetrad_. The arms of the chromatids now get tangled up and recombine in a new order called crossing over. Next during anaphase 1 the sister chromatids separate with their _centromeres_ intact! Two daughter cells are produced during telophase 1.
  • 2nd division: similar to mitosis but now the chromatids separate during telophase 2 creating 4 haploid cells. Single strands of chromosomes are captured in each cell.


Gametogenesis: The creation of sex cells either eggs or sperm by meiosis

Female gametogenesis occurs in the ovaries. Called oogenesis.

It forms one viable egg and _3_ tiny polar bodies.

Male gametogenesis creates sperm in the testes. Called spermatogenesis.

It creates _4_ viable sperm from one orginal cell.



During mitosis, the genetic code of the cells is always _1_N (one gene set is from the egg and the other from the sperm).

After meiosis, the genetic code is _1/2_N (only 1/2 of the normal number of genes are present).

This is called Haploid or _monoploid_ .

After fertilization, the genetic code of the cell is restored to _2_N or Diploid.



Sex cell
Gonads (male and female)
Sister Chromatids
Polar bodies
Crossing Over

Essential Questions:

  1. Where does meiosis take place?
  2. What is the difference in chromosome number of a somatic cell compared to a sex cell (gamete)?
  3. Why is it important for meiosis to result in 1/2 the normal number of DNA?
  4. Why is meiosis called reduction division?
  5. Why is it a genetic advantage for a species to undergo meiosis and then fertilization as opposed to vegetative reproduction?
  6. What does haploid vs diploid mean?
  7. How is spermatogenesis different from oogenesis?
  8. How does meiosis differ from mitosis?