In assembling a nucleosome, normally the …(1) histone dimers first combine to form a tetramer, which then further combines with two … (2) histone dimers to form the octamer.

option 1

Explanation:

In assemblying the nucleosome, this reaction occurs in two main steps. the H3 and H4 are recruited first to the DNA in pairs forming the H3/H4 tetramer; meaning two of H3 and two of H4. This gives rise to the nucleosome precursor. Then after this, the dimers of both H2A/H2B are recruited to this precursor, to give rise to the octamer structure around which the DNA is wrapped.  

the abdomen (less formally called the belly, stomach, tummy or midriff) constitutes the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. the region occupied by the abdomen is termed the abdominal cavity. the stomach secretes acid and enzymes that digest food. ridges of muscle tissue called rugae line the stomach. the stomach muscles contract periodically, churning food to enhance digestion. the pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.

cell regulation is conducted by special proteins.