Genes are mostly located in chromosomes but also in mitochondria, chloroplasts and plasmids

Chromosomes are found in the nucleus of a eukaryote and in the cytosol a prokaryote.

Aneuploidy

• extra chromosomes but not a set 
• eg., trisomy 2N +1, monosomy 2N-1
• trisomy 21: 2N +1 (Down’s Syndrome)
• Klinefelter syndrome XXY (extra X chromosome)
• may result from non disjunction in meiosis at anaphase 1 or 2 (i.e both chromosome go to one cell and don’t split into 1 in each cell.

Euploidy

• extra sets -polyploidy 
• eg., triploid (3N), tetraploid (4N)
• triploid bananas, tetraploid grapes (extra chromosomes in cells so fruit is bigger)
• Triploidy in humans is not compatible with life