Autosomal and Z‐linked genetic evaluation for body weight in Mazandaran native chicken using different models for dosage compensation on the Z chromosome

Abstract

The objectives of this study were to assess the autosomal and sex-linked genetic inheritance of growth traits and identify the effective dosage compensation on the Z chromosome in Mazandaran native chickens. The data included body weights at hatching (BW0), 8 weeks (BW8) and 12 weeks (BW12) of age, related to the first 21 generations of selection, were collected from Mazandaran native chicken breeding centre. The fixed effects included sex of birds in two classes, hatch in five classes and generation in 21 classes. The inverse of the sex-linked additive genetic relationship matrix was constructed using nadiv package in R considering different models for dosage compensation on the Z chromosome. The setup inversed matrix was then supplied externally to WOMBAT using the GIN option. Twelve univariate animal models separating participation of autosomal additive genetic, sex-linked additive genetic and maternal effects (both genetic and permanent environment effects) with considering the five different dosage compensation methods for models with sex-linked effects were analysed by WOMBAT software. BW0 was not affected by sex-linked additive genetic effects.For BW8 and BW12 the model which included autosomal, sex-linked direct additive and maternal effects with no global dosage compensation for the Z chromosome was the most appropriate model. Autosomal heritability estimates were 0.05 ± 0.02, 0.10 ± 0.01 and 0.11 ± 0.01, for BW0, BW8 and BW12, respectively.For BW8 and BW12, sex-linked heritability estimates were 0.07 and 0.27, respectively. Spearman rank correlation coefficient between autosomal and sex-linked breeding values were 0.45 and 0.12 for BW8 and BW12, respectively. Spearman rank correlation coefficient between autosomal and sex-linked breeding values were 0.45 and 0.12 for BW8 and BW12, respectively. The autosomal direct additive genetic correlations between all traits were positive. The estimate of direct sex-linked additive genetic correlation between BW8 and BW12 was high (0.88). Also, maternal genetic correlations were 0.53, 0.54 and 0.91 between BW0-BW8, BW0-BW12 and BW8-BW12, respectively. Given the importance of Z-linked genes for BW8 and BW12, it is recommended that Z-linked effects be separated from autosomal effects in order to increase the accuracy of genetic evaluation of birds for these traits.

Sex‐specific genetic parameter estimates of body weight in Mazandaran indigenous chickens

“…We found no significant contribution of the covariance between direct and maternal genetic effects to the studied traits. Several studies have reported negative direct‐maternal genetic covariance to be significant (Gholizadeh & Hafezian, 2022; Kaviani et al., 2023). The negative direct‐maternal genetic covariance can be caused by the negative direct‐maternal environmental covariance which is usually neglected in genetic evaluation (Robinson, 1996) maybe because the environmental covariance is not straightforward to include in the genetic models using common software.…”