Sentence:  Homozygous and heterozygous * * f cells , * * f and homozygous and heterozygous * * f cells were used to test each <WSD>sample</WSD> ; however , in the interest of clarity and conciseness only the results obtained with homozygous * * f and homozygous * * f cells will be presented here . 
Meaning of the word marked with <WSD> tags:  a small part of something intended as representative of the whole