Child has a disease that is causing severe growth delays and rapid aging. His cells are assayed, and it is noticed that there is a severe decrease in DNA synthesis compared to normal cells. When DNA from his cells was gently heated to separate the double helix, numerous, small, single-stranded fragments of about 1000 base pairs were found. Which enzyme is likely to be defective in this child

DNA ligase

Explanation:

DNA ligase is an enzyme that responsible for the joining of two DNA strands by the formation of a bond between the deoxyribose group of one DNA strand and the phosphate group of the other DNA strand. DNA ligase is responsible for sealing recombination fragments, connects okazaki fragments formed during DNA replication and also sealing DNA during repairs.

DNA ligase deficiency also referred to as ligas 4 syndrome is characterized by  severe growth delays, combined immunodeficiences and abnormal facial structure.

Therefore, in the case of this child with this disease, the enzyme likely to be defective is DNA ligase.

it also supports my hypothesis. if you rest first you can squeeze the clothespin more times. from the data i collected the average of the eight people concluded exercise makes your muscles more fatigued and less able to squeeze the clothespin compared to resting before squeezing.