What is the difference between chromosome mutation and gene mutation? explain with examples (one page)

Gene mutation:

Gene mutation may be defined as change or alteration in the nucleotide sequence of the gene.  DNA replication errors and mutagens are responsible for the gene mutation. A single gene may affected in this mutation. For example: Sickle cell anemia is caused by the replacement of GAG to GUG results in the formation of valine instead of glutamic acid. The shape of RBCs changed from the biconcave to the sickle cell shape.

Chromosome mutation:

Chromosome mutation may be defined as the change or the alteration of chromosome number or structure. Chromosome mutation occurs due to errors during crossing over. The segment of the chromosome may get changed. Large number of genes may get affected. For example: Down syndrome occurs due to the presence of extra chromosome at chromosome 21.