As a biologist working with a cell culture, you notice that the ends of the chromosomes are decreasing in size after each cell division. Other than that, the cells seem healthy. What is the most likely explanation?

In the given case, it can be concluded that very less amount of telomerase is being produced.

Explanation:

Terminal transferase or telomerase refers to a ribonucleoprotein that supplements a telomere repeat sequence to the 3 prime terminals of telomeres. A telomere is present at each terminal of the chromosomes found in the majority of eukaryotes. It helps in safeguarding the terminals of the chromosomes from destruction or from getting combined with the adjacent chromosomes.  

Telomerase has its own RNA molecule and works as a reverse transcriptase enzyme. Generally, telomerase is found active in gametes, in stem cells, and in the majority of cancer cells, however, it is generally present in low concentration or is absent in the majority of somatic cells. Thus, the decrease in the ends of the chromosomes suggests that the production of telomerase is taking place at low levels.  

tissue

explanation:

it is actually formed by geoup of cells which is tissue