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 PF1 - average PP/ PP , measured in units of the trait

PF1 = average performance of crossbreds

PP = 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 - (ps1pd1 + ps2pd2 + psnpdn)]F1HV

 ps1 = proportion of breed 1 in sire

pd1 = 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: