If you’re reading results that have been printed on a sheet of paper, you can skip this step. Not all stains require UV-light for visualisation. Check which stain you used and how to properly visualise it (for example, some dyes may be activated by blue light, or are readily visible without need for any special lights).
There should be one well for each of your samples. If one of the wells is lacking color, the sample may have been applied poorly. The wells indicate the negative end of the sheet. The opposite side of the sheet is the positive end. When each sample is applied to the sheet, the negatively-charged DNA travels across the sheet to the positive pole.
If you performed the test yourself, write down where each row’s sample is from while you’re applying the gel.
Actual DNA samples will have a lot of variation in the sequence of the strips. There may be a few thin strips, followed by 1–2 inches (2. 5–5. 1 cm) of empty space, followed by thick strips, and ending in more thin strips. The DNA ladder will make it easier to figure out how big the individual strips actually are by giving you something to compare them to. The DNA ladder is almost always placed in the last row at the top or bottom of your sheet.
The way individual strips are arranged in a sequence is unique to each genetic sample. The pattern of strips creates a specific picture of someone’s genetic makeup. The thickness of each band is not an indication of how long the DNA molecules are, but of how many there are.
1000 bp is the same as 1 kb. Kb is short for kilobase, and the ladder may use this unit instead of bp. The smaller the scale is, the more accurate the comparisons will be. Base pairs and kilobases are simply units of measurement. They refer to the physical size of a DNA molecule.
In other words, if you’re looking at the sheet with the wells on the left, you’re looking for vertical columns where 2 strips appear at the same time. For example, a mother and her child will have half of their strips overlapping. A child and their second cousins though may only have 2-3 strips that overlap.
More than 2 overlapping bands indicates a strong similarity between 2 samples. When assessing results, scientists will often say that there is a “high probability” that 2 samples are related if less than half of the bands in 2 samples overlap.
