What are restriction enzymes? in gel electrophoresis the dna fragments are separated according to why do the largest dna fragments not move very far? in step 7, what does the term hybridize mean? what is the purpose of the dna probe hybridizing to the dna strand?

Restriction Enzymes
                                 These enzymes are produced by bacteria. they have the ability to cleave DNA fragment a specific recognition site. They are also known as restriction endonucleases or molecular scissors. On the basis of sub unit composition, cleavage position, sequence specificity and co-factor requirements they are classified into four groups.

In gel electrophoresis DNA fragments are separated according to size. Large DNA fragments not move very far because of their large molecular size they can not travel.
In this case hybridize mean to measure the degree of genetic similarity between two pools of DNA sequence.

Purpose of DNA probe hybridization
                                                               Hybridization probe is 100-1000 bp long strand which is radioactively labelled. It is used to determine the presence of nucleotides in DNA which is complementary to sequence in DNA probe.