Interesting+Notes+and+Original+Table

The terminal end buds were only measured in the young virgin rats, but why? As mentioned in the anatomy and dynamics section, as rats (and people) age the breast continues to develop and those TEB structures will also differentiate and branch. While TEBs were found in old virgin rats, it is likely that there were not enough of the cells in order to preform a complete cell cycle experiment. Instead they measured the TDr or terminal duct regression structures. If the female never becomes pregnant or delivers a child some of the differentiated structures will regress. This is where TEBs may be located, but they most likely do not make up a majority of these structures. This is supported by the fact that parous rats, whose breast never have to go through the regression process, only have terminally differentiated structures. While the data is included for all phases of the cell cycle, the only one that we are interested in the the G1 phase. This is the phase responsible for repairing the type of DNA induced by our carcinogen so while there is more interesting data in the other cell cycle phase lengths, they are not crucial to our discussion. As you can see the length of each cell cycle for each structure is essentially the same across the board excluding the G2 phase. My best guess as to why the G2 phase of parous rats is longer in OV rats would be that it compensates for the incredibly short G1 phase. If our theories are correct and more damage can be repaired in the G1 phase of parous rats, perhaps the OV rats have adapted by increasing their G2 phase. If mutations are allowed to pass though G1 they will likely result in DNA damage or mutations during the process of replication in S phase. In order to compensate for the potential increase in mutations/DNA damage perhaps the longer G2 phase (which is primarily utilized as a checkpoint and timer for un-repaired DNA damage to be fixed) acts in a similar manner as the lengthened G1 phase in order to increase the amount of time to catch mistakes before the cell proceeds with mitosis. Call it your last line of defense.