Is it due to attachement of bronken part of one chromosome to another. I hope this helps.
The answer is A:
The SUGAR-PHOSPHATE CHAINS form the sides, and the BASE PAIRS form the rungs
Absorbing prokaryotic cells. This theory is called the endosymbiotic theory.
The early prokaryotic cells that were absorbed likely evolved into mitochondria and chloroplasts, membrane-bound organelles with their own DNA in single chromosomes and their own ribosomes.