Most accepted theory of heterosis

a) Dominance theory

b) Over-dominance theory

c) Epistasis theory

Types of chromosomal aberrations

A. Structural aberrations

1. Deletion
2. Duplication: Bar eye
3. Inversion: Partial pollen sterility and occurs frequently in natural population.

i. Paracentric inversion: Centromere not present in inverted segment

ii. Pericentric inversion: Centromere present in inverted segment

4. Translocation

B. Numerical aberrations : Also called as heteroploidy

a. Aneuploid; Not exact multiple of chromosome number.

1. Nullisomic; 2n-2 ; one pair missing
2. Monosomic : 2n-1; one chromosome missing
3. Double monosomic; 2n-n-1-1
4. Trisomic; 2n+1; one pair extra
5. Double trisomic: 2n+1+1
6. Tetrasomic: 2n+2

b. Euploid: Exact multiple of chromosome number

I. Monoploid: x

ii. Haploid : n

iii. Polyploid: >2

a. Autopolyploid: More than two copies of a single genome ( tri-3x, tetra = 4x)

I. Autoctaploid: 8x

b. Allopolyploid: ≥ 2 genome

I. Allotetraploid; 2x₁ + 2x₂

ii. Allohexaploid: 2x₁ + 2x₂ + 2x₃

iii. Alloctaploid: 2x₁ + 2x₂ + 2x₃ + 2x₄

Note: Most inbreeding are annual and do self-pollination.