Chevalet, C

Rastogi, R

English

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Chevalet C

Rastogi R

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Genetics Selection Evolution

On methods of estimation of maternal heterosis and recombination effects from a specific three breeds crossing system

R Rastogi

C Chevalet

Springer

R. RASTOGI

C. CHEVALET

EDP Sciences OAI-PMH repository (1.2.0)

ON METHODS OF ESTIMATION OF  MATERNAL HETEROSIS AND RECOMBINATION  EFFECTS FROM A SPECIFIC THREE BREEDS  CROSSING SYSTEM

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NOTE
ON METHODS OF ESTIMATION OF
MATERNAL HETEROSIS AND RECOMBINATION
EFFECTS FROM A SPECIFIC THREE BREEDS
CROSSING SYSTEM
R. RASTOGI C. CHEVALET
Laboratoire de Genetique des Petits Ruminants,
* Labovatoive de Génétique Cellulaire,
Centre de Rechevches de Toulouse, I. N. R. A.,
B. P. 12, 31320 Castanet Tolosan
SUMMARY
The present note is an extension of DICKERSON’S(A. B. A., 1969, 191-202) paper. Three
different methods for the estimation of maternal heterosis from a specific 3-breed crossing system
were evaluated for possible biases. Method II was found to provide most nearly an unbiased esti-
mate of maternal heterosis (h M). For example,
It was further suggested that the same data could be used to estimate epistatic recombi-
nation effects.
DICKERSON (1969) stated, « Near maximum performance is expected in the best 3-breed
cross of superior sire breed with crossbred females of 2 other breeds having the best economic
combinations of F, maternal and transmitted performance characteristics n. This will be gene-
rally true for those offspring characteristics that are influenced by indirect maternal effects such
as, growth. Thus, to maximize and to accurately predict immediate gains from a specific 3-breed
crossing system a knowledge of the magnitude of maternal heterosis and epistatic recombination
effects is essential.
The present note is an extension of DICKERSON’Spaper and here we briefly review different
methods used to estimate maternal heterosis for their merits and limitations. It is further sug-
gested that the same data can also be used to arrive at estimates of epistatic recombination effects.
DEFINITIONS
Let mean performance of three breeds be represented by letters A, B and C, respectively.
Further assume that all possible pure breeds, 2- and 3-breed crosses are produced contempora-
neously. Then,
Ai = individual heterosis and is the mean deviation in the performance of 2-breed crosses
from the average performance of pure breeds due to increased average heterozygosity of Fls,
plus any epistatic interaction between purebred parental gametes.
h M = maternal heterosis and is the same as hI but for indirect maternal effects of F! cross-
bred dams. It is a measure of average dominance interaction deviations in maternal effect (m)
of F, dams relative to that of purebred dams, for example
hP = paternal hetevosis and is analogous to h M but for indirect paternal effects.
r! = epistatic recombination effects and is the deviation due to change in epistatic gene
interaction effects in 3-breed crosses, relative to those in 2-breed crosses, from recombinations
between gametes derived from parent breeds of F, crossbred sires or dams.
The parameters-h M,hP and Y’ are specific effects of crossbred dam’s or sire’s genotype but
are measured as environmental effects from analyses of offspring data.
EVALUATION OP’ VARIOUS METHODS
Various comparisons used to estimate maternal heterosis and epistatic recombination
effects have been summarized in the following table along with their genetic expectations. No
attempt has been made to explicitely derive these expectations. However, it can be easily accom-
plished in closely following DicxExsorr (ig6g).
To arrive at these expectations and to obtain unbiased estimates certain assumptions must
be made ; the critical ones are :
a) linkage equilibrium and randomness of mating.
b) interaction effects involving three or more loci are negligible.
c) additive (no interaction) combination of genetic and heterotic contribution of different
breeds in various crosses, for example :
that is, environmental effect is the same for all breed groups (purebred, 2- and 3-breed cross).
d) no interaction between genetic contribution of the sire and the maternal ability of the
dam. Such interaction might arise if a sire gave his offspring genetic growth potential that was
incompatible with the milking ability of the dam.
e) no confounding with differences in proportion of multiple births ; sex ; year, season
and date of birth ; heterosis in male (h a) and female (h?) reproductive performance.
f) rI = o (applicable only to method I).
g) hP = o.
In species like swine, sheep and rabbit, use of individual observations will lead to less precise
estimates of h M due to confounding of differences in proportion of multiple births between
crossbred and purebred dams. The estimates of h M and rI will be further less precise if h 3 and
h! was of significance. In mathematical sense, these estimates will be unbiased but will not
necessarily have minimum variance.
If only three breeds were involved, method III could not provide specific estimates of hM
for each kind of crossbred dam and method II should be the choice if unbiased estimates were
desired. However, if four breeds were involved in the production of 3-breed crosses it should
be possible to obtain specific estimates of h M, for example.
where D represents the fourth breed. For this comparison to be true one must further assume
that there is no interaction between the genotype of the offspring (C(AB), D(AB)) and that of the
crossbred dam (AB). This is an extension of method II utilizing information on both possible
3-breed crosses.
The various comparisons listed in table i should be applicable to reproductive traits, such
as litter size at various ages, for estimating hg and h 3.
Re!u pour publication en août 1973.
RÉSUMÉ
A PROPOS DES MÉTHODES D’ESTIMATION DE 1/HÉTÉROSIS MATERNEL
ET DES EFFETS DE RECOMBINAISON DANS UN SYSTÈME
DONNÉ DE CROISEMENTS A TROIS RACES
Cette note est une extension de l’article de DtcxExsorr 196g). Trois méthodes sont compa-
rées pour estimer l’hétérosis maternel à partir d’un plan systématique decroisements entre trois
races. Les sources possibles de biais sont considérées ; la méthode II fournit l’estimation la moins
biaisée de l’hétérosis maternel. Par exemple :
On indique par ailleurs que les mêmes données pourraient être utilisées pour estimer les effets
de recombinaison.
REFERENCES
DtcxExsoN G. E., 1969. Experimental approaches in utilising breed resources. Anim. breed. Abstr.,
37, 191-202.
DICKERSON G. E., 1973. (Personal Communication).


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On methods of estimation of maternal heterosis and recombination effects from a specific three breeds crossing system

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