MITOSIS & MEIOSIS


Website:
http://www.accessexcellence.org/RC/VL/GG/mitosis.html
http://www.accessexcellence.org/RC/VL/GG/meiosis.html
http://biowiki.wikispaces.com/Mitosis-Meiosis
http://onlinebiotext.wikispaces.com/Mitosis
http://biologyeoc.wikispaces.com/Meiosis

Mitosis is a process of cell division that produces two daughter cells from a single parent cell. The daughter cells are identical to one another and are also identical to the original parent cells. Mitosis can be divided into four stages. The first stage is prophase. This is where the chromatin condenses into chromosomes. Each chromosome has duplicated and now consists of two sister chromatids. At the end of prophase the nuclear envelope breaks down. The second stage is metaphase. This is when the chromosomes align themselves in the center of the cell and are held in place by the microtubules which is attached to the kinetochore. The third stage is anaphase. The centromeres divide and the sister chromatids separate and move toward the poles. The fourth stage is telophase. The daughter chromosome arrives to the pole, the microtubules disappear, the chromatin unwinds, and the nuclear envelope reappears. Afterwards, cytokinesis occurs which is when the cytoplasm divides and thus producing two daughter cells.


Meiosis consists of two successive nuclear divisions with only one round of DNA replication. At first the genetic material are duplicated which is during the interphase. After during prophase 1, the chromatin condenses and each chromosome consist of two sister chromatids. Cross-over occurs in the latter part of this stage. Then in metaphase 1, the homologous chromosome aligns in the middle of the cells. In the anaphase 1, the homologous pair is separated. In the telophase 1, the daughter cells are formed with each daughter containing one chromosome of the homologous pair. Then during prophase 2, the DNA does not replicate. In metaphase 2, the chromosome aligns in the middle of the cell. In anaphase 2, the centromeres divide and the sister chromatids migrate to the poles. Finally in telophase 2, cells division is complete and four haploid daughters are formed.

external image C1.meio2.gif
http://lc.brooklyn.cuny.edu/smarttutor/core3_21/images/meiosis/C1.meio2.gif
external image Mitosis.JPG
http://www.uhh.hawaii.edu/~ronald/392/Mitosis.JPG