Chromosome Mutations
a change in the structure of all or part of a chromosome 
or in the number of chromosomes

deletion/insertion/inversion/translocation/nondisjunction

	Deletion  occurs when a piece of a chromosome breaks off, resulting in the loss of some genes
	Insertion (addition) happens when a piece of  a chromosome breaks off and attaches to a homologous pair (thereby getting a repeating piece)
	Inversion   occurs when a piece of a chromosome is rotated, which reverses the order of genes in a the chromosome
	Translocation is the transfer of a part of a chromosome to a nonhomologous chromosome

Nondisjunction 
the addition or loss of an entire chromosome.  

This occurs when homologous pairs (tetrads) do not separate properly during Anaphase I of Meiosis.  This failure to separate chromosomes properly leads to a condition in which the offspring has an abnormal number of chromosomes.  The condition of having an extra chromosome in one of it pairs is called trisomy (a human with trisomy would have 47 chromosomes instead of 46).  When an organism is missing one of its chromosomes, the condition is called monosomy (a human would have 45 chromosomes) .

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