12 Genetics, Cells, and Chromosomes 



dragged along passively by the centromeres. After the chroma- 

 tids have begun to pull apart, they are referred to as daughter 

 chromosomes. 



Anaphase begins as soon as the centromeres begin to move to 

 the poles and ends when all the centromeres have arrived at the 

 poles. Although the initial movement is probably always due 

 to the repulsion of the centromeres, the final movement is some- 

 times accomplished by an elongation of the central part of the 

 spindle after the two groups of daughter chromosomes have 

 progressed part of the way towards the poles. 



Telophase. As soon as the two groups of chromosomes, with 

 the centromeres in advance, have arrived close to the poles, a 

 nuclear membrane begins to form around each group and finally 

 completely encloses it. At this stage, the cell has two new 

 nuclei, but the remains of the spindle still persist between them. 

 At the equator, each spindle "fiber" begins to liquefy, and finally 

 a thin fluid area is found extending completely across the cell. 

 This plate cuts the cell into two complete halves, and where the 

 cytoplasm comes in contact with this liquid plate, a plasma 

 membrane is formed. The cytoplasm is now divided into two 

 parts, and each part has a new nucleus. 



The changes in the nucleus during telophase are practically 

 the reverse of those during prophase. After the nuclear mem- 

 branes have formed around the groups of daughter chromo- 

 somes, the chromosomes themselves become extremely long and 

 thin, and are consequently less deeply stained. Part of this 

 process is due to a loss of the matrix which had collected during 

 prophase around the threads. The nucleolus or nucleoh reappear 

 and become large as telophase progresses. After these changes 

 are concluded, each new daughter nucleus resembles the resting 

 nucleus of the original cell. 



Significance of Mitosis 



If the plant we were studying was the onion, there were 16 

 chromosomes in the resting stage' of the cell before division. At 

 prophase, each chromosome consisted of 2 chromatids so that 

 there were 32 chromatids. As anaphase separation took place, 

 the 2 chromatids of each chromosome became new chromosomes 

 so that, during anaphase, there were 32 chromosomes, 16 of 

 which went to each daughter cell. Therefore, each new cell has 



