Help explain my DNA bands smearing

[Elizabeth Bates]

Dear Netters,
Of course everybody's right on this question. Genomic DNA when cut with 
'normal' restriction enzymes ie type II frequent cutters should give a 
smear. However genomic DNA also consists of non-random repeats such as 
satellite DNA, Alu sequences etc. These show up on restriction digests 
as unique bands and can be used to control the digestion. So a digest 
which has completely cut should show a smear and superposed onto this a 
series of enzyme- and species-specific bands. Hope that this helps to 
resolve your doubts :-).
Liz.