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