Why is the exact replication of dna needed

*THE MOST SIMPLE EXPLANATION I CAN PROVIDE* DNA has a certain combination of nitrogenous bases (adenine [A], thymine [T], guanine [G] and cytosine [C]). During the process of 'translation' DNA is copied to mRNA. Then in the subsequent process of 'transcription' mRNA goes into ribosomes, a tRNA comes and attaches to the mRNA. each tRNA has three bases that must be complementary to the mRNA base. Also at the top of the tRNA is a amino acid. Then the next tRNA for the next three bases come and so on (the three bases is called a codon). As the tRNA attached to the mRNA the amino acids on top of each tRNA attach to each other like train carriages. Eventually this stops and a chain of amino acids of produced. Long story short, a number of amino acids makes proteins. Proteins can be enzymes significant to metabolic pathways or useful themselves. For example melanin is the skin pigment protein.

Now, if the DNA replication was not exact then the mRNA would reflect that of the inexact DNA. The codon with the tRNA for the mRNA in the ribosome may not be available that tRNA may not have the correct amino acid and hence a certain protein may not be produced. For example, the disease Epidermolysis bullosa (EB) is cause when a certain protein is missing that leads to the production of connective tissue present between the skin and underneath. Hence for people with EB there skin fall off (children with this disease are often called 'butterfly children').

DNA copying in multicellular organism isn't appropriate that leads to variations in individuals and much more chance of survival of a particular species.Is it not important for a progeny to have exact copy of DNA of their parents.Only in single celled organism DNA copying is mostly correct.