Final answer:
The commercial HinIII fragments and the student-generated fragments are used to estimate the size of PCR products and verify the accuracy of restriction digestion, using the commercial standards as a reference point.
Step-by-step explanation:
The purpose of using commercial HinIII fragments of lambda DNA in lane 4, as well as those generated by the student in lane 1, is for comparison and validation purposes. Commercial HinIII fragments are known size standards that act as a reference for the fragments generated in the experiment.
By comparing the experimental fragments to the commercial standards, the student can estimate the size of their PCR products and verify the accuracy of their restriction digestion.
Additionally, using a DNA ladder in the first lane is essential for size determination, as it contains DNA fragments of known sizes, facilitating the estimation of the PCR fragment sizes in other lanes. This process is crucial in experiments such as genomic library creation, RFLP analysis for DNA fingerprinting, and sequencing wherein accurately determining the size of DNA fragments is fundamental.