Euploid chicken embryos from eggs containing one, two or several yolks

Area of Science:

• Reproductive biology
• Avian genetics
• Developmental biology

Background:

• Large chicken strains exhibit high rates of haploid/diploid chimerism.
• This chimerism is hypothesized to stem from erratic ovulation patterns in hens selected for large size.

Purpose of the Study:

• To investigate the relationship between erratic ovulation and the incidence of heteroploidy in chicken embryos.
• To determine the specific mechanisms leading to chromosomal abnormalities in embryos from multiple-yolk eggs.

Main Methods:

• Karyological analysis of chicken embryos from eggs with single or multiple yolks.
• Eggs were sourced from a chicken line selected for multiple ovulation over 20 generations.
• Fertility and survival rates of ova in multiple-yolk eggs were compared to single-yolked eggs.

Main Results:

• Multiple-yolk eggs showed significantly lower fertility and embryo survival rates.
• The incidence of triploidy (3n) was significantly higher in multiple-yolk eggs (7.0%) compared to single-yolk eggs (0%).
• Digynic origin (two maternal pronuclei) was the predominant cause of triploidy, linked to suppressed second polar body extrusion.

Conclusions:

• Erratic ovulation, indicated by multiple yolks, suppresses second polar body extrusion, leading to digynic triploidy in chicken embryos.
• Multiple yolks did not influence dispermy, the cause of 1n/2n chimerism in single-yolked eggs.
• Reproductive irregularities in large-sized chicken strains are significantly associated with specific forms of embryonic heteroploidy.