Silent mutations change the nucleotide sequence of the DNA, yet the protein sequence is unchanged. This is due to the redundancy of the genetic code. Missense mutations involve substitution of one amino acid instead of another, which could change the folding pattern of the polypeptide. Nonsense mutations involve substitution of a nucleotide that results in a stop codon rather than the appropriate amino acid. This results in a truncated protein, which is nonfunctional. Frameshift mutations involve insertions, deletions and/or duplications of nucleotides. This shifts the reading frame on the mRNA, resulting in a nonfunctional protein. Note that frameshift mutations in which multiples of three nucleotides are inserted, deleted and/or duplicated are do not change the reading frame, and may still yield a functional protein. However, for example, a deletion of two nucleotides does change the reading frame and would lead to a nonfunctional protein.

The red blood cells are still made, but their shape is different. This can be caused by a missense mutation, the replacement of one amino acid by another. A nonsense mutation would produce a truncated protein, which most likely would not be functional at all. An insertion or deletion could cause a frameshift mutation which could produce a completely different protein. Nondisjunction refers to meiosis, not DNA replication.

Evolution relies on genetic diversity. One source of genetic diversity is spontaneous mutation. One spontaneous mutation may be beneficial to an organism's fitness, increasing the chance of that mutation being passed to the next generation.

Mutations are not always harmful as they can also be beneficial. Keep in mind mutations are also not always beneficial. Mutation simply is a process that produces new alleles in genes due to mistakes made during recombination, DNA replication or repair. 

The central dogma of molecular biology states that DNA is transcribed into RNA, which is then translated into protein.

The human genome can code for 64 different codons, but only produces 20 different amino acids. This results in some amino acids having multiple codes in order to use the remaining 44 available codons.

This ability of a single amino acid to have more than one possible codon is called "degeneracy." Occasionally when DNA is mutated, it will results in a codon that encodes the same amino acid. For example, a mutation from CUU in the mRNA sequence to CUG will still code for leucine.

DNA nucleotides are organized to form codes. When DNA is transcribed into RNA, these codes are read by the ribosomes to create proteins. Each gene refers to a sequence of DNA that codes for a specific protein. Mutation to a specific gene will affect that protein coded for by that sequence.

A locus is the location of a gene on a chromosome, and an allele is an alternative form of a given gene. A genotype is the description of the alleles for a specific set of genes.

Following the P generation is the 1st offspring generation, called F1. When the F1 generation is crossed, the result is the 2nd offspring generation, called F2.

G1 and G2 actually refer to periods of growth during the cell cycle, and are not related to genetics and inheritance.

A gene codes for a certain protein product, which is often associated with a certain trait. Each gene is found at a specific location, or locus, on a chromosome.

Alleles refer to different forms of DNA that can appear at the same locus. In other words, an allele is an alternative form of a given gene. Different alleles often result in different phenotypes, such as changes in color or size.

Eukaryotes possess coding (exon) and non-coding (intron) seqeunces that allow for incredibly long DNA sequences to correspond with relatively short peptides. Only the exons are translated after the mRNA sequence, which is transcribed fully from the DNA, undergoes mRNA splicing. Furthermore, while a codon (three nucleoties) does correspond with one amino acid, it does not account for the dramatic difference stated in the question. Also, the cell does not translate an entire unmodified mRNA sequence and cleave afterwards as that would be incredibly wasteful and potentially harmful to the cell.