What would be the difference between a gene mutation and a chromosomal mutation?

A gene mutation can be described as errors in the nucleotide sequence of a gene due to errors in the DNA replication process or due to any mutagen. On the other hand, a chromosomal mutation can be described as a change in the structure of a DNA or changes in the number of chromosomes.

A gene mutation occurs in a single gene whereas a chromosomal mutation will affect many genes. Hence, gene mutations will be comparatively less lethal than chromosomal mutations.

Example of gene mutation: Sickle cell anemia

Example of chromosomal mutation: Down's Syndrome