Bioguard Corporation
Many mammals are sexually dimorphic, which means that their sex can be identified based on their appearance. However, it is not the case for most birds. Many birds are sexually monomorphic although males and females may differ markedly in size, color, and appearance in some birds, such as peacocks (Fig. 1).
Knowledge of a bird’s gender is important for veterinary practitioners, ornithologists and aviculturists. Gender identification in birds is beneficial for proper pairing of birds, and preparing owners for the eventual changes their bird will experience as it matures. Furthermore, knowing the gender of a bird allows veterinarians to diagnose gender-specific diseases.
Traditional sexing
The traditional methods used to identify a bird’s gender include behavioral observation, morphological differences, acoustic analysis, laparoscopic examination, laparotomy, vent sexing (cloacal examination), steroid sexing, and chromosome inspection (karyotyping). These methods can be inaccurate, invasive, or costly. As an alternative to these methods, molecular DNA-based sexing methods provide fast, accurate and non-harmful to the bird.
DNA sexing
The XY sex-determination system is used to classify many mammals, some insects (Drosophila), and some plants (Ginkgo tree). In this system, most females have two of the same kind of sex chromosome (XX), while most males have two distinct sex chromosomes (XY).
The sex of birds is determined by the ZW sex determination system. Females have the heterogametic sex chromosomes ZW, whereas males have the homogametic ZZ.
The standard method of molecular sexing in birds relies on PCR amplification of non-coding sequences (introns) located in the sex-chromosome-specific gene encoding the Chromo-Helicase-DNA binding protein (CHD1), and mapping on the sexual W (CHD-W) and Z chromosomes (CHD-Z). The length polymorphisms between CHD-W and CHD-Z alleles allows for sex discrimination. Amplification of the CHD gene leads to a single amplicon in males and two distinct amplicons in females.
In addition to PCR, other PCR-based technologies have been applied to avian sexing, including Single Strand Conformation Polymorphism (SSCP), Restriction Fragment Length Polymorphism (RFLP), and Amplified Fragment Length Polymorphism (AFLP). These methods, however, are not viable for commercial use.
Conclusion
