Exponential expansion

mikeflower

[FONT=&quot]I've got a cell line with a gene that gets bigger exponentially.[/FONT]
[FONT=&quot]I cultured the cells from 16/1/17 for 295 days and the gene expanded exponentially. For the second culture, cells from culture 1 frozen on 22/5/17 (d127), were thawed on 2/1/18 and cultured for 196 days. For the third culture, cells from culture 2 frozen on 1/3/18 (d59), were thawed on 7/5/18 and cultured for 64 days.[/FONT]
[FONT=&quot]Curve estimating in SPSS gives [/FONT]

[FONT=&quot]C = 121.10 x e^(0.000547 x d)[/FONT]

[FONT=&quot]Where C is the gene length in days and d is the number of days in culture. r2 = 0.989, p = 7.65E-26.[/FONT]

[FONT=&quot]When you plot them on a graph, taking d0 as the starting date of each culture, they intersect at 109 on the y axis, which I know is the original gene length.[/FONT]

[FONT=&quot]Can I please ask a) is my interpretation of the intersect correct, b) is my explanation of the data in the correct nomenclature?

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MacstersUndead

Note the following:
* y-axis for your graph precisely means the vertical line of Days = 0. Each of your exponential curves intersects the y-axis at different values.
* I would make the distinction that Day 0 is the start time when the cultures were observed and the data points were collected.

It would be more correct to say the following about the intersection point of the three exponential curves.
"If we assume that we can extrapolate these three curves to the past, then these curves attain the same approximate Modal CAG Repeat Length of 109 [units] at around Day = -200."

The crux is the if, though in the domain of gene study, it might be a reasonable assumption.

mikeflower

Thank you. When I offset the start date by how long they've been in culture (essentially now day 0 is the start of culture 1, and cultures 2 and 3 start the day they were frozen form the preceding culture), the exponential rates don't overlap. Successive cultures seem to increase faster, which is not what I would expect.
I was a little surprised that the original lines all intersected at 109 on the y axis, though as this is a biologically relevant size, I think it must be meaningful. I'd be grateful for your help with interpretation.
Thanks

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MacstersUndead

Based on the most recent graph you've given, it looks like all three curves, which represent trends extrapolated from measured data points from Day 0, intersect at around the same y-value of 130 at Days = 150.

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