Hybrid Vigor - Heterosis

Hybrid Vigor or Heterosis: An increase in the performance of hybrids over that of purebreds, most noticeably in traits like fertility and sterility (Crossbreeding definition).

Hybrid Vigor or Heterosis: An increase in the performance of hybrids over that of purebreds from linebred families, most noticeably in traits like fertility and sterility (linebreeding definition).

Is a result of increasing Gene Combination Value.

P = m + G + E = m + BV + GCV + E

BV = independent genes

GCV = gene interactions which yields heterosis.

Example of Heterosis:

Measuring Hybrid Vigor

HV = average P_F1 - average P_P/ P_{P ,} measured in units of the trait

P_F1 = average performance of crossbreds

P_P = average performance of parents lines = P₁ + P₂/2.

Examples of measuring Hybrid Vigor:

Components of Hybrid Vigor

Individual Hybrid Vigor: Hybrid vigor for the direct component of a trait.

Maternal Hybrid Vigor: Hybrid vigor for the maternal part of the trait.

Paternal Hybrid Vigor: Hybrid vigor for the paternal component of the trait.

Examples:

Maintenance of Hybrid Vigor

F₁ Hybrid Vigor: The amount of hybrid vigor attainable in first cross individuals = maximum hybrid vigor.

Retained Hybrid Vigor (RHV): Hybrid vigor remaining in later generations of hybrids - generations subsequent to the first cross (F₁) generation.

Calculating Retained Hybrid Vigor (RHV):

Simply inherited traits - measure heterozygosity with gene frequency in F₁ vs F₂.

 Polygenic traits -

 RHV = [1 - (p_s1p_d1 + p_s2p_d2 + … p_snp_dn)]F₁HV

 p_s1 = proportion of breed 1 in sire

p_d1 = proportion of breed 1 in dam

F₁HV = typical F₁ hybrid vigor for the trait

Example: 

Backcrossing to Retain Heterosis

Backcrossing: The mating of a hybrid to a purebred of a parent breed or line.

Example: