الفهرس 
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Abstract
The experimental work of the present study was conducted at the Poultry Research Center, Poultry Production Department, Faculty of Agriculture, Alexandria University, Egypt, during the period January 2020 and May 2021.
Two varieties of quails, Japanese (JJ) and White (WW) were selected (S) for high body weight at 6 weeks of age for three generations. An unselected random bred control (C) for each variety was used. This study comprised 5 generations (base and 4 generations).
In the third generation of selection both selected varieties (Japanese and White) were crossed. The breeding plan permitted the simultaneous production of purebred genotypes (J x J, W x W) and crossbred genotypes (J x W, W x J).
In generation 4, backcross was applied between the purebred genotype (WW) as
males with the crossbred (WJ) as females beside the other crosses. The breeding plan permitted the simultaneous production of purebred genotypes (J x J, W x W) and crossbred genotypes (W x J, W x WJ).
The aim of this study was to evaluate the response of selection for body weight at 6 weeks of age for growth traits. Also, to evaluate heterosis, additive and reciprocal effects
for growth and fitness traits after crossing between the two selected varieties of quails. In addition, to evaluate the effect of backcross between selected purebred with the crossbred
genotypes on growth traits.
The obtained results of this study could be summarized in the followings:
The interactions between generations (0-3) and lines (S & C) for BW and BWG at all ages (0, 2, 4, and 6 wks) studied were significant for both varieties (JJ & WW).
After three generations of selection for BW6 in both varieties, the S line was significantly heavier than the C line. Means of BW at 6 wks of age for the S line of JJ and WW varieties were 270.62 and 281.54 g, respectively. The
corresponding means for the C line were 226.05 and 224.91 g.
Regression analysis cleared that there were significant increases in BW at 0, 2, 4, 6 wks and BWG at 0-6 wks of age over 3 generations of selection for high body weight in the S line (0.5, 13.7, 15.5, 11.6, and 11.5 g/generation, respectively) for JJ and (0.5, 9.8, 18.5, 16.4, and 15.9 g/generation, respectively) for WW. While
regression coefficients of BW and BWG on generations at the corresponding
ages for the C line were not significant.
After three generations of selection for high BW at 6 wks of age, the cumulative realized responses were 36.68 g in males, and 49.55 g in females for Japanese quails, and 44.07 g in males, and 60.24 g in females for White quails.
All realized heritability estimates for BW at 6 wks of age of Japanese and White quails were high. The cumulative realized heritability estimates over generations of selection were 0.55 for males, 0.64 for females, and 0.54 for combined sexes in Japanese quails. The corresponding heritability estimates were 0.65, 0.73, and 0.67 in White quails.