HETEROSIS RETENTION AND INTER-BREED RECOMBINATION AMONG NONALLELIC GENES ASSOCIATED WITH CROSSBREEDING AND SYNTHESIS OF BREEDS

ABSTRACT
Systematic crossbreeding and newly developed synthetic populations based on
complementary breeds of exotic and/or indigenous origin, in conjunction with selection
for specific objectives among economically important traits has consistently expedited
rapid genetic improvement of production efficiency along with the income and
profitability of the livestock and poultry enterprises. The breakdown of desirable
combinations of segregating alleles inherited from many of the parental breeds during
crossbreeding or the development of synthetic populations could lead to loss of
desirable morphological characteristics and production performance. This may be
attributed to the inter-breed recombination among non-allelic genes (epistasis)
decreasing the proportion of retained heterosis, both direct and maternal. In addition to
recombination loss, selection over subsequent generations increase the loss of within
breed variability, decrease effective population size and hasten the rate of inbreeding.
Research results on recombination loss in the parents and their offspring have often
been conflicting. Precise estimates require large numbers of breeds and their crosses
independent of environmental influence. The objective of the present study is to
discuss crossbreeding strategies capable of retaining heterosis in the following
generations while enhancing genetic merit of parents and their offspring.