Answer
A difference in polarity during the assembly process causes the changes in severity of the mutations.
Work Step by Step
The triple helix rod design is formed from collagen monomers that start in their amino-terminal ends. These rods are typically long in nature. If a mutation occurs early on the glycine before it becomes an acid the mutation will result in a shorter rod, as compared to if the mutation occurred later which result in somewhat longer, more normal rods.
