The size of DNA fragment or the gene of interest could be estimated using standard markers (like 1kb, 100bp markers etc.). If our fragment run between the known marker fragment, then this method is useful.

1. Calculating the size of DNA fragments
using unknown marker length
Nishanth Sekar
PhD (Ag) in Microbiolgy

2. Problem:
Calculate the size of A, B, C using the Hind III digest of lamba DNA marker
Create standard curve using DNA marker
Measure distance travelled by unknown
DNA fragment
Determine size of DNA fragment
Size of unknown A, B, C
?
!

3. Create standard curve using DNA marker
Size of DNA fragment in
bp
log 10
Distance travelled by
the fragments (cms)
23130 4.3642 4.4
9416 3.9739 5.0
6557 3.8167 5.9
4361 3.6396 7.1
2322 3.3659 9.2
2027 3.3069 9.8
564 2.7513 14.8
125 2.0969 17.5

4. Measure distance travelled by unknown
DNA fragment
Distance travelled by A = 6.5 cm
Distance travelled by B = 10.7 cm
Distance travelled by C = 13.7 cm

5. Determine size of DNA fragment
A
B
6.5 cm 10.7 cm 13.7 cm
2.7
3.2
3.8
A : antilog (3.8) = ~ 6309 bp
B : antilog (3.2) = ~ 1585 bp
C : antilog (2.7) = ~ 501 bp
C

6. Using MS Excel
Simple linear regression equation
y = mx+c
In this case…
y = -0.149x+4.792
Size of DNA fragment in
bp
log 10
Distance travelled by
the fragments (cms)
23130 4.3642 4.4
9416 3.9739 5.0
6557 3.8167 5.9
4361 3.6396 7.1
2322 3.3659 9.2
2027 3.3069 9.8
564 2.7513 14.8
125 2.0969 17.5
Distance
travelled
(cms)
Value of y Antilog
A 6.5 3.8235 6660.395
B 10.7 3.1977 1576.522
C 13.7 2.7507 563.2483
Trendline !!!
Size of A, B and C