Genetic sex-typing



For approximately 50 per cent of the 10,000 bird species on earth, the sexes are indistinguishable and individuals look alike, even as adults.

There are genetic markers available to sex some species of birds but these do not work for all groups of species and sample types. Some sample types can be particularly problematic e.g. shed feather or museum footpads.

To overcome the limitations of exitsing markers I developed new markers for sexing birds based on the CHD, ZSWIM and Spindilin gene. In total, I have been involved in the genetic sex-typing of over 200 species of bird. 

Details of new sex-typing markers I developed are below:

Marker Z37B (Dawson et al. 2015) amplifies a small product and is suitable for sex-typing degraded samples (eg museum samples, unhatched eggs) and samples of low quantity (eg feathers, mouth swabs).

Marker Z43B (Dawson et al. 2016) is able to sex species that are problematic to sex with other markers.

I have collected data relating to the protocols needed to sex different species from another 100 species. Some markers detect Z chromosome polymorphism which needs to be considered when interpreting sexing data  
(Dawson et al. 2001). We have found that birds from the same family can normally be sex-typed using the same primer set and technique.

Therefore I have created a webpage and database to assist researchers in becoming familiar with the techniques involved in molecular bird sexing and to indicate the most suitable choice of method to use for a particular species. See the "See Also" section. This work was discussed in my PhD thesis.


For some mammal species, it is not possible or difficult to distinguish between males and females, for example  shrews, cats and Eurasian otters.

Other species are difficult to study because they are rare, elusive or nocturnal and in these cases, non-invasive samples, such as faecal samples or hair, can be used to identify the presence of different individuals and their sex.

I worked with Dr Marion Huck to developed a new sex marker for badgers Meles meles (Huck et al. 2008) and with Kate Denton to develop a sex marker suitable for sexing various species of bat (Denton 2020, manuscript in prep.).


Dawson DA, Darby S, Hunter FM, Krupa AP, Jones IL and Burke T (2001) A critique of CHD-based molecular sexing protocols illustrated by a Z-chromosome polymorphism detected in auklets (Aves: Alcidae, Laridae). Molecular Ecology Notes, 1, 201–204.

Dawson DA, Brekke P, dos Remedios N, Horsburgh GJ (2015) A marker suitable for sex-typing birds from degraded samples. Conservation Genetics Resources, 7, 337–343 [Open Access].

Dawson DA, dos Remedios N, Horsburgh GJ (2016) A new marker based on the avian spindlin gene that is able to sex most birds, including species problematic to sex with CHD markers. Zoo Biology, 35, 533–545. [Open Access]

Bat sexing marker is described within this work:

Denton K. (2020) PhD Thesis (University of Greenwich, NBAF1049) [The potential of insectivorous bats as agents of crop pest control in the UK]

Badger sexing marker is described within this work:

Huck M, Frantz AC, Dawson DA, Burke T, Roper (2008) Low genetic variability, female biased dispersal and high movement rates in an urban population of Eurasian badgers (Meles meles). Journal of Animal Ecology, 77, 905–915.

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