Question

Mouse genomic DNA is treated with a restriction endonuclease and electrophoresed in an agarose gel. A radioactive probe made from the human gene rxr-1 is used to perform a Southern blot. The experiment was repeated three times. Explain the results of these repeated experiments:

Experiment 1. The autoradiogram shows a large smudge at a position corresponding to the top of the lane in which the mouse DNA was electrophoresed.

Experiment 2. The autoradiogram shows a smudge over the entire lane containing the mouse DNA.

Experiment 3. The autoradiogram shows three bands of varying intensity.

Answer

Short answer

The result of experiment 1:In Experiment 1, the restriction enzyme failed to cut mouse DNA into short sequences.

The result of experiment 2:Experiment 2 shows that the renaturation standards were not followed to the letter.

The result of experiment 3: Experiment 3 demonstrates that three sequences in the mouse rxr-1 gene are identical to those in the human rxr-1 gene. In the band with the highest intensity, the gene with the most similarity is detected.

Step-by-step solution

Result of experiment 1

Southern blotting is a technique for determining specific DNA sequences. The principal method relies on nitrocellulose's ability to bind single-stranded DNA.

Experiment 1 revealed that the restriction enzyme was unable to break down mouse DNA into little bits. The fragments were too large to fit through the gel matrix. Because of this, the radioactive probe only hybridized at the top of the lane, resulting in a big patch.

Result of experiment 2

The second experiment revealed that the hybridization conditions were not strictly adhered to. It's possible that the required sequence moved all over the sheet because mouse DNA didn't link to nitrocellulose strongly enough. DNA is usually dried at$80°\text{C}$to keep it in place forever.

This might also happen if a high amount of labeled probe was used, resulting in nonspecific probe hybridization to all DNA segments.

Result of experiment 3

The probe bound to three different mouse DNA sequences, according to the results of the previous experiment. The mouse DNA sequence that is most comparable to the human rxr-1 gene is found in the most intense band.

Therefore the experiment reveals that the mouse gene has three sequences that are identical to the human rxr-1 gene. The gene with the most similarity is found in the band with the highest intensity.