B. B. Bohren

Relative Efficiencies of Heritability Estimates Based on Regression of Offspring on Parent

The problem of optimal estimation of the coefficient of regression of offspring on parent (in the sense of minimum variance), when the number of progeny per parent is arbitrary, was completely solved by Kempthorne and Tandon [1953]. Prior to this paper, two methods were (and still are) commonly used: (1) the regression of the phenotypic mean of all offspring of a given parent on the parents record; (2) the regression of offspring on parent, in which the parents record is repeated for each of its progeny. Kempthorne and Tandons technique, which they refer to as (3) the weighted regression technique, assigns weights to the progeny means which are functions of the number of progeny and a guessed value of a correlation coefficient p between deviations from regression associated with two progeny of the same parent. The difficulty here lies in the fact that p is unknown. The success of the general technique depends upon guessing p accurately. Presumably if the guessed value of p is close to p, the weighted technique is close to optimal. The precise effect of a poor guess for p does not seem to be known. The purposes of this paper are (1) to investigate the nature and magnitude of the correlation coefficient p, and (2) to compare the efficiencies of the various techniques with respect to data from a population of poultry.

Direct and correlated responses to selection for hatching time in the fowl 1

Synopsis Selection over eight generations for a shorter (fast hatching) or longer (slow‐hatching) incubation time in fowls resulted in a difference of 42 h in incubation time. Only minor asymmetry of response was observed since incubation time decreased by 19.8 h in the fast‐hatching line and increased by 22.4 h in the slow‐hatching line. The predicted response was less than that observed, probably because of underestimation of the true selection differentials and a low estimate of heritability used for prediction. The realised heritability estimates decreased significantly from 0.222 to 0.179 between the first four and the last four generations. The estimate based on all eight generations was 0.199. These values are probably slightly overestimated because of the use of underestimated selection differentials in their calculation. The realised heritability in the original stock was probably between 0.20 and 0.25. No evidence of correlations between hatchability or egg weight and hatching time was obtained....

Combining ability among single grosses and predicting double cross performances in poultry 1 2

Synopsis Thirteen traits were examined on progeny of 40 egg‐type double crosses sampled over 2 years in order to evaluate the importance of general and specific combining ability variances among single cross parents in double cross combination and the feasibility of predicting double cross performance from parental and non‐parental single crosses. General combining ability variance was significant for 8‐and 55‐week body weight, egg shape index, egg weight, percentage egg production, meat spots and adult mortality, while specific combining ability variance was not significantly different from zero for any traits. General combining ability variance was not significant for age at first egg, interior egg quality, specific gravity and blood spots. Multiple regression procedures using as independent variables ordered means of parental and non‐parental single crosses and inbreds yielded higher predictability of double cross performance than using the respective means of each set. Deletion of parental single cros...

A test for linkage of the loci for dominant white and barring with loci controlling growth rate in the fowl 1

Synopsis Females from a coloured inbred line of Leghorns (ii) were mated to three groups of males heterozygous for the dominant white gene (Ii). The parents transmitting the I gene to the three groups of males were respectively larger, smaller and of the same size as the parents transmitting the i gene. No differences were observed between the three types of crosses in the effect of colour genotype on body weight, providing no evidence for linkage between the dominant white locus and loci affecting body weight. When comparisons were made between the colour genotype classes, pooled within full sib groups, the coloured genotype was larger in ten of the twelve test cross‐sex‐hatch combinations. Two of these differences, were statistically significant, but when the data were pooled over hatch, sex and test cross, no significant difference was found. The data thus offer meagre support for weight differences in favour of the coloured genotype, but the negative evidence of the pooled analysis raises considerable...

Performance of lines selected for fast‐and slow‐hatching times and crosses among them 1

1. Males of a control line and two lines selected for fast‐ and slow‐hatching were mated to females of the same three pure lines and three crosses between them. Hatchability, egg weight and hatching time were measured. 2. No significant differences were found between genetic groups in hatchability. 3. Groups containing the fast‐hatching line genotypes were significantly smaller in egg weight than those not containing this line. 4. Significant differences in hatching time existed between male lines and between female lines within pure and cross‐line parent types while no differences were observed between the female parent types and no interactions of male by female lines occurred. 5. It was concluded that inbreeding in the pure lines (10%) did not affect any of the variables measured. 6. The results on hatching time support the conclusion that little genetic variance other than additive variance is involved for this trait.