|Chromosomes (red) being dragged toward the metaphase plate. Image: Ted Salmon, NIH|
But as mitosis begins, the nuclear envelope starts to break up and disappear. Each chromosome has replicated during interphase and is therefore composed of two sister chromatids containing identical genetic information.
Early during prophase, the first stage of mitosis, the chromosomes become visible with a light microscope as they condense (that is, as they shorten, coil, and thicken). Also, a spindle apparatus (blue strands in the upper two figures at left) begins to extend outward from each of the two centrosomes. These starlike configurations, composed of radiating microtubules, are also known as asters — Greek for stars — (see photomicrograph of asters >>).
It's "PROH-faze," not "PROP-faze."
A silly poem to help you remember:|
Mitosis happens everywhere, even in my toe,
Meiosis only happens in my OH!
|Mneumonic device: You can remember the first letters of each of the stages of mitosis in order (together with interphase) by remembering one of the following three sentences: "I picked my apples today." OR "I passed my anatomy test." OR "I prefer my Aunt Tillie." Take your pick.|
|Note: No tetrads form during mitosis.|
|Prometaphase. Some teachers like to distinguish a fifth stage of mitosis called prometaphase, which corresponds to that portion of mitosis occurring after the disappearance of the nuclear envelope, but before arrival of the chromosomes at the metaphase plate.||The spindle apparatus >>|
|DNA replication >>|
|Sister chromatids >>|
|Nuclear envelope >>|
Human Origins: Are we hybrids?
On the Origins of New Forms of Life
Cat-rabbit Hybrids: Fact or fiction?
Georges Cuvier: A Biography
Prothero: A Rebuttal
Branches of Biology