Determination of Sex in Domestic and Wild Animals and Birds
18.4.1 Determination of Foetal Sex
A number of biotechnological tools and imaging techniques can be applied to determine foetal sex in animals during the various period of embryonic life (Table 18.3).
The biotechnological tools identify sex-specific genes, amplicon, enzymes and proteins. Ultrasonography is the best imaging technique to determine foetal sex through phenotypiccharacteristics. The identification of males is more accessible than the females by molecular markers like sry gene using polymerase chain reaction (PCR) based sexing assays. The embryos can be sexed by DNA probes specific for the Y chromosome (H-Y antigen) or assayed for X-linked enzymes using the fluorescent antibody technique (FAT). The embryo sexing is useful in multiple ovulation embryo transfers (MOET) nucleus breeding schemes to generate more economic animals, avoid freemartins multiple births, develop transgenic and cloned animals, and conserve wildlife (discussed details in Chap. 24).
Table 18.3 Recognition of differentiation of foetal sex in different domestic animals and birds
| Species | Duration from post-fertilization (week) | Mode of identification/genetic markers | Reference |
| Cattle | 5-7 | Y-specific sequences | da Cruz et al. (2012) |
| Cattle | 4-34 | sry gene; Y-specific amplicons | Xi et al. (2006), Wang et al. (2010); da Cruz et al. (2012) |
| Cattle | 7-16 | Ultrasonography | Quintela et al. (2011) |
| Cattle & Horse | 9-10 | Ultrasonography | Curran (1992) |
| Horse | 4; 8-20 | sry gene; sry& GAPDH | De Leon et al. (2012); Davoodian and Kadivar (2016) |
| Goat | 5 | Amelogenin gene | Chen et al. (2007) |
| Goat | 6-17 | Ultrasonography | Amer (2010) |
| Sheep | 8-18 | sry gene & GAPDH; Amelogenin gene | Kadivar et al. (2013); Davoodian and Kadivar (2016) |
| Pig | 2 | sry gene | Pomp et al. (1995) |
| Dog | 4-7 | sry gene & Ultrasonography | Prugnard et al. (2016) |
| Dog | 3-4; 8 | Ultrasonography | Orlandi et al. (2019); Khatti et al. (2018) |
| Cat | 6 | Ultrasonography | Zambelli and Prati (2006) |
| Mouse | 2 | sry gene | Larney et al. (2014) |
| Mouse | 1 | Ultrasonography | Pallares and Gonzalez-Bulnes (2009) |
| Bird | 1 | DMRT1 gene | Chue and Smith (2011) |
Phenotypic characteristics are employed to determine postnatal sex in domestic and wild animals. But, it is difficult in birds, as most birds are monomorphic. Vent sexing is a common process in birds (discussed details in Chap. 19).
18.4.2 Determination of Sex in Birds
Different molecular techniques like karyotyping and PCR are generally used to differentiate sex in birds. Homologous ZZ chromosomes confirm that the male and ZW chromosomes validate females. The expression profile of the DMRT1 gene through PCR is used to identify male birds. Amplifying chromodomain helicase DNA-binding (CHD) gene, producing one amplicon fragment of the Z chromosome, confirms male, where two fragments for the Z and W chromosomes confirm the female birds.
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Sex Determination in Monotremes
The sex-determining region on the chromosome Y (sry or, sry gene) presents in all mammals, except the animals, viz. platypus, echidnas, steropodon, etc. under order monotremes. Monotremes are placental mammals and nurture the young by their milk but lay eggs. Monotremes comprise distinctive XY sex chromosome systems with several homologies with the avian Z chromosome.
18.5