Supercoiling of pure circular DNA is a result of__（）
A. underwinding or overwinding of the helix
B. the long length of the strands
C. the lack of associated histones
D. the activity of exonucleases
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Which of the following is an example of highly-repetitive DNA（）
A. Globin gene family
B. Histone gene cluster
C. Minisatellite DNA
D. rDNA gene family
Watson & Crick won the noble prize in 1962 for their discoveries concerning（）
A. the interaction between tumour viruses and the genetic material of the cell
B. the mobile genetic elements
C. the molecular structure of nucleic acids
D. the invention of the PCR method
It is easier to melt DNA richer in AT than GC because（）
A. it is more heat sensitive
B. there is one less hydrogen bond in an AT base pair
C. the helix pitch is longer in AT rich regions
D. All of the three statements
What are the target and the probe of the Southern blotting（）
A. DNA, DNA
B. RNA, RNA
C. Protein, antibody
D. None of the above
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