Sex mammals

Sex determination in mammals

The list of available tests of sex in mammals

The sex determination in mammals is genetic. If females and males differ in their appearance, they are designated as sexually dimorphic. Besides the different sex organs, the dimorphic individuals differ also in secondary features, such as colour, size and shape. In species without sexual dimorphism or in less distinctive young animals, genetics can be used to determine the sex. The sex identification by the method of molecular genetics is of great benefit to animals as they are not stressed by invasive sex examination. The genetic test is quick, available and reliable.

In general, the mammals have two sex chromosomes X an Y. In placental mammals incl. humans the males develop due to the male-dominant effect of the sex chromosome Y. The Y-chromosome contains approx. 1400 genes and belongs to medium-size mammal sex chromosomes (~155 Mb). The X-chromosome contains not only genes responsible for the development of female reproductive organs and reproduction, but also genes responsible for the brain function. On contrary, the human Y-chromosome is smaller than X-chromosome and contains approx. only 45 active genes. The Y-chromosome carries in particular specific genes having effect on the development of the male organs in XY embryos – one of these genes is SRY-gene (sex-determining factor Y). The mammalian XY-chromosomes have obviously developed from an ancestral pair of autosomes, independent on the avian Z- and W-chromosomes. The primitive egg-laying (oviparious) mammals (Prototheria) have a greater number of sex chromosomes; the females of duckbilled platypus have 5 X-chromosomes and the males have the same number of Y-chromosomes.

During the embryonic development stage, the sex of an individual can be affected by genetic factors or, in some cases, by environment. We can also see this phenomenon for example in reptiles, where the sex is determined by the temperature during the egg incubation.
The SRY-genes (sex-determining factor Y), ZFX/Y (zinc finger protein), AMELX and AMELY (amelogenin) are genes used to determine sex by the methods of molecular genetics in humans and placental mammals.

In case of primitive mammals, specific regions of autosomes, by which the both genders differ, are used to determine the sex. The sex can be identified either directly by sequence analysis or fragment length polymorphism analysis (RFLP).

Very often, the presence of the species-specific SRY-gene or the differences in the sequence of AMELX and AMELY are determined. The genes for amelogenin and ZFX/Y are exceptional as they are present both on X and Y chromosomes and differ only in their sequence.

Reference:

Aasen E, Medrano JF (1990) Amplification of the ZFY and ZFX genes for sex identification in humans, cattle, sheep and goats. Biotechnology (N Y) 8(12):1279–1281. doi:10.1038/nbt1290-1279

Hošek P.: Bodlíni nejsou jen bodlinatí aneb první savci na Madagaskaru, Vesmír 83, 2004: 215-219

Pagès M., Maudet C., Bellemain E., Taberlet P., Hughes S., , Hänni C. A system for sex determination from degraded DNA: a useful tool for palaeogenetics and conservation genetics of ursids, Conservation Genetics, August 2009, Volume 10, Issue 4, pp 897-907

Safrova, M., Blahova, B., Dajbychova, M., Saskova, K., Stampachova, K.: Molecular genetic analysis of sexual diversities in Spiny Tenrecs. Poster 33rd conference of the International Society of Animal Genetics (ISAG)

Sen Song; Liang Liu. Resolving conflict in eutherian mammal phylogeny using phylogenomics and the multispecies coalescent model. PNAS (Proceedings of the National Academy of Sciences of the United States of America ), 28. srpen 2012, svazek 109, čís. 37, s. 14942-14947.

Shaw C, Wilson P, White B (2003) A reliable molecular method of gender determination for mammals. J Mammal 84(1):123–128.

Stephenson, P.J. (2007). Mammals from another time: tenrecs in Madagascar. Africa Geographic, March 2007, Vol 15 (2): 34-41

Tariq Ezaz, Rami Stiglec, Frederic Veyrunes, and Jennifer A. Marshall Graves: Relationships between Vertebrate ZW Review and XY Sex Chromosome Systems, Current Biology 16, R736–R743, September 5, 2006

http://www.afrotheria.net/ASG.html

http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi