Question

The figure shows the restriction enzyme cutting sites $(R1-R3)$ in wild type $(n)$ and mutant $(n)$ gene.

If a radioactively labelled probe (that hybridises at a sequence close to $R1$) is used for detecting the presence of $DNA$ fragments after gel electrophoresis and Southern blotting, which of the following band patterns will your expect?
Note : $L1$ : wild type $DNA$, $L2$ : mutant $DNA$

• A.
• B.
• C.
• D.

Answer 1

Answer: (C)

Restriction enzymes recognise the base sequence of palindrome sites in $DNA$ duplex and cut its strands. After the cutting of $DNA$ by restriction enzymes, fragments of $DNA$ are formed. Separation of $DNA$ fragments according to their size is done by gel electrophoresis. Since the probe hybridises close to $R1$ it will give $500kb$ band for $L1$ and $400kb$ band for $L2$ after gel electrophoresis.