Most genetic mutations result in spontaneous miscarriages and never see phenotypical expression. The majority of genetic mutations that do see physical expression are deleterious and result in early death or lifelong health problems for the individual carrying the allele. A tiny minority of mutations prove to be beneficial and can then spread through a breeding population.
That is true but many, if not most, genetic mutations result in a flaw that leads to a dead-end on that limb of evolution. The saber- toothed Tiger being one example.
No, the snake evolved over time. The rattle became smaller and smaller over time until it no longer had one.
Take the Santa Catalina rattlesnake for example.
After reading up on it, is believed that mutation/evolution occurred because of hunting purposes. Making it quieter. I originally thought it was for survival.
A nice example of a 'mutation' that is phenotypic can be seen in this petunia. This is actually not a normal 'mutation', but caused by a transposon aka a jumping gene. There are pieces of DNA that can 'transpose' themselves in the genome. In this case it 'jumped' right into one of the genes for color in this flower and basically in random cells, which gives this flower it's pattern of red on white. Each flower would have it's own pattern as the transposition is basically random. I used to study the genetic regulation of the forming of flowers in Petunia in my thesis 20 years ago.