title: A reliable method for sexing unincubated bird eggs for studying primary sex ratio.
abstract: In birds, offspring sex ratio manipulation by mothers is now well established with potentially important consequences for evolution and animal breeding. In most studies on primary sex ratio of birds, eggs are sexed after incubation by the use of PCR methods targeted to the sex-linked CHD1 genes. Sexing of unincubated eggs would be preferred, but as fertile and infertile blastodiscs cannot be distinguished macroscopically, errors could arise from PCR amplifications of parental DNA associated with the vitelline membrane of infertile eggs. In this study, we stained blastodiscs without the vitelline membrane with Hoechst 33342. This allowed unequivocal distinction between fertile and infertile blastodiscs. Fertile blastodiscs contained thousands of fluorescent nuclei, whereas no nuclei were seen in infertile eggs. In addition, after nucleic acid analysis, fertile blastodiscs yielded much stronger chromosomal DNA and CHD1-targeted PCR bands on agarose gels compared with infertile blastodiscs. These findings indicate that fertile blastodiscs contain much more embryonic DNA than parental DNA, allowing reliable sexing of the fertile eggs. The differences between fertile and infertile blastodiscs in chromosomal DNA and CHD1 PCR banding intensities alone could also be used to distinguish fertile from infertile eggs without using Hoechst staining. We conclude that identifying fertile blastodiscs either by Hoechst staining or by analyzing the yield of chromosomal DNA and CHD1-PCR products, combined with CHD1-targeted PCR amplification, presents an easy and reliable method to sex unincubated eggs.
authors.affiliation: Animal Breeding and Genomics Centre, Wageningen UR Livestock Research, PO Box 65, 8200 AB Lelystad, The Netherlands.
authors.forename: M Aamir
authors.initials: MA
authors.lastname: Aslam
authors.forename: Marcel
authors.initials: M
authors.lastname: Hulst
authors.forename: Rita A H
authors.initials: RA
authors.lastname: Hoving-Bolink
authors.forename: Agnes A C
authors.initials: AA
authors.lastname: de Wit
authors.forename: Mari A
authors.initials: MA
authors.lastname: Smits
authors.forename: Henri
authors.initials: H
authors.lastname: Woelders
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000235:genetics; D001562:Benzimidazoles / Q000378:metabolism; D001717:Birds / Q000196:embryology*; D054239:Blastodisc / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics; D005456:Fluorescent Dyes / Q000378:metabolism; D016133:Polymerase Chain Reaction / Q000379:methods; D012732:Sex Determination Analysis / Q000379:methods*; D012744:Sex Ratio; D013194:Staining and Labeling / Q000379:methods*
chemical_list: D030161:Avian Proteins; D001562:Benzimidazoles; C489845:CHD-W protein, Gallus gallus; D004268:DNA-Binding Proteins; D005456:Fluorescent Dyes; C017807:bisbenzimide ethoxide trihydrochloride