Question

Which property of DNA double helix led Watson and crick to hypothesize Semi-Conservative mode of DNA replication? Explain.

Answer 1

Hint: As we already know that genes are nothing but small sequences of DNA, deoxyribonucleic acid compact in long strands of DNA. Many strands of DNA form chromosomes and they are tightly packed with proteins inside a cell. Genes contain all the information which is being carried out from generation to generation. Hence, gene library refers to the collection of genes.

Complete answer:
DNA fragments are sequences of DNA which are cut by restriction enzymes and are stored in agarose gel. Agarose gel is a medium in which DNA travels towards an electrode to show banding. This process is termed as gel electrophoresis. The technique is used to determine DNA size.
Watson and Crick hypothesize the semi-conservative mode of DNA replication. As DNA contains two strands which are complementary to each other but also, they can be antiparallel also. Complementary strands mean one head part of a strand having a $5'$ hydroxyl group and the end part or the other strand having a $3'$ group. In any DNA strand the strands initiating the template specially show-case this hydroxyl group.
DNA sequence is stored in long sequences and maintained in data bank. DNA sequences are placed in compact structures. Semi-conservative mode of replication is- copying from partially parent strand and new strand of DNA. Conservative on other hand led to replication from parent template strand.
One strand of parent and new strands replicate to form the new copy strand. The arrangement from $5'$ to $3'$ however remains the same. This is how DNA replicates from one DNA to other DNA.

Note:
The DNA strands however are complementary to each other like- A, T, G, C that is adenine pair with thymine and guanine pairs with cytosine. One such is- cDNA libraries, genomic libraries and random mutant libraries. DNA libraries are basically constructed by adding genes of interest to DNA fragments which have been cleaved by restriction enzymes. Everyone has a separate genome for their purpose.