Gametic fusion - aneuploid conditions
1. n x (n-1) - 2n-1(monosomic condition)
2. (n-1) x (n-1) - 2n-2(nullisomic condition)
3. n x (n+1) - 2n+1(trisomic condition)
4. (n+1) x (n+1) - 2n+2(tetrasomic condition)

Examples of aneuploidy -

Monosomy - Turner's syndrome

Trisomy - Down's syndrome, Klinefelter's syndrome