Dissection of X chromosome dosage compensation for quantitative traits in sheep using different statistical models

Area of Science:

• Animal Genetics
• Quantitative Genetics
• Sheep Breeding

Background:

• Males and females have different numbers of X chromosomes, necessitating mechanisms for gene dosage equalization.
• Understanding X chromosome dosage compensation is vital for accurate genetic parameter estimation in livestock.

Purpose of the Study:

• To investigate X chromosome dosage compensation for growth rate (GR), Kleiber ratio (KR), efficiency of growth (EF), and relative growth rate (RGR) in Zandi sheep.
• To compare different models of X chromosome dosage compensation and their impact on genetic evaluation.

Main Methods:

• Employed a two-step animal model procedure, selecting the best model using AIC.
• Fitted additional models incorporating five strategies for X chromosome dosage compensation.
• Assessed model predictive ability using Mean Squared Error of Prediction (MSE) and Pearson's correlation.

Main Results:

• Models including X-linked effects significantly improved data fit (AIC) and predictive ability (MSE, correlation) for GR and KR.
• The 'no global dosage compensation' (ngdc) model provided the best fit for GR and KR among compensation strategies.
• Inclusion of X-linked effects reduced autosomal additive variance and residual variance for GR and KR.

Conclusions:

• Accounting for X-linked genetic effects and dosage compensation improves the accuracy of genetic evaluations in Zandi sheep.
• Re-ranking of top animals was observed when X-linked effects were included, highlighting their importance.
• Incorporating X-linked genetic effects into breeding models is recommended for GR and KR in Zandi sheep.