Is there just one strand (extremely long) of DNA in a single human Chromosome?
I ask because some books show a chromosome as a structure with 4 'arms' -
2 short and 2 long - with bands which can be shown up by biological stains.
These pictures seem to show symmetrical staining on the 2 similar arms eg
on the long arms. Does that mean that the 2 arms are completely identical
at the chemical sequence level? If so, are there 2 stands of DNA in each
chromosome? (one in each arm).
More biochemical books show the DNA of the Chromosome as a single 'line'
pinched in at the 'waist', with marked sites at which endonucleases act.
Please explain simply, to put me out of my misery !
--Peter Hulbert, ---p.b.hulbert at bradford.ac.uk