A section of whitefish blastula at 400x
Why are whitefish blastula used to study mitosis? The blastula is an early stage of embryo development and represents a period in the organism's life when most of the cells are constantly dividing. Moreover, the dividing cell have very large and easily seen chromosomes, so its easy to find lots of cells in each stage of mitosis.Human chromosomes on the other hand, are are not clearly visible at higher power magnification. So, for student purposes, whitefish blastula are used.
Whitefish blastula cells in interphase
The three phases of Interphase
Whitefish blastula cells in early prophase
Whitefish blastula cells in metaphase: the cell on the left is in early metaphase, the cell on the right in late metaphase
A whitefish blastula cell in anaphase
During anaphase the mitotic spindle apparatus pulls the sister chromatids of each chromosome apart by attaching to each centromere and then pull the chromatids to each pole of the cell. Note that the telomeres of each chromosome point toward the cellís equator.
A whitefish blastula cell in telophase + cytokinesis
Chromosomes begin to disperse. Spindle fibers disperse. Cytokinesis begins--formation of daughter cells. In animals, like the whitefish, a cleavage furrow, a contractile ring of muscle like fibers, pinches the cell into two. The nuclear envelope forms again around the nuclei.
Whitefish Mitosis Practice