As B-DNA is gradually heated, the absorbance at 260 nm（）
A. increases
B. decreases
C. stays the same
D. It is unpredictable
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Histones are found in close association with DNA. Which of the following statements is incorrect（）
A nucleosome core is composed of ~146 bp of DNA and a histone octamer
B. Histone H1 binds to linker DNA
C. There are only four types of histones
D. Nucleosomes are evenly distribution within chromatin
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
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
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