Additive and testcross genetic variances in crosses among recombinant inbreds

R. Bernardo, W. E. Nyquist

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Breeders desire populations with a high mean performance and a large genetic variance. Theory and methods are lacking for predicting additive variance (V(A)) and testcross variance (V(T)) in biparental populations. Breeders have unsuccessfully attempted to predict V(A) based on the coefficient of coancestry (f) or molecular-marker similarity between parents. In this paper, we derive the expected values of V(A) and V(T) in biparental populations, examine the variability of V(A) among biparental crosses, and discuss how V(A) and V(T) may be predicted in applied breeding programs. Suppose i is a recombinant inbred derived from the cross between inbreds P1 and P2, and inbred j is not a direct descendant of i. Let V(A(i,j)) be the additive variance in the F2 of the (i x j) biparental cross. Let V(T(i,j)) be the variance among testcrosses of F2 individuals with a specific unrelated inbred or population. Assuming linkage equilibrium and the absence of epistasis, V(A(i,j)) = λ V(A(P1, j)) + (1 - λ) V(A(P2, j)), where λ = parental contribution of P1 to i. Similarly, V(T(i, j)) = λ V(T(P1, j)) + (1 - λ) V(T(P2, j)). Additive variance in crosses between recombinant inbreds cannot be modelled as a function of f if, as indicated in the literature, V(A) differs among crosses of founder inbreds. If molecular-marker similarity between parents is used as an estimate of f, then a strong linear relationship is likewise not expected between V(A) and marker similarity. Differences between the actual and expected λ led to variation in V(A). In applied breeding programs, modelling V(A) or V(T) in biparental crosses may be feasible with estimates of V(A) or V(T) in prior crosses and information on λ obtained from molecular-marker data.

Original languageEnglish (US)
Pages (from-to)116-121
Number of pages6
JournalTheoretical And Applied Genetics
Issue number1-2
StatePublished - Jul 1 1998


  • Additive variance
  • Inbreeding
  • Recombinant inbreds
  • Testcross variance


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