Sex Threesome

Typical sex may no longer be an X-Y thing

It is commonly believed that when you ask for a female dog, you generally will receive a bright eyed puppy with female genitals and a lovely disposition. However, in the case of the American cocker spaniel, this is not always so. All too often people are receiving ‘female’ puppies that are either hermaphrodites or males with bilateral testes.

In mammals, sex-determination is thought to be exclusively associated with the Y-linked SRY-gene, as it is responsible for testis induction. Therefore, any animal with XY genes will display male genitals, while those with XX will be female. However, animals with chromosomes 78, XX have been found to be true hermaphrodites with ovotestes, or XX males with bilateral testes. Originally it was thought that a mutation had occurred that translocated the SRY-gene onto an X-chromosome. Further studies however revealed that these animals were actually SRY-negative, leading to the naming of the disorder as SRY-negative XX sex reversal.

Pedigree data from two separate studies suggested that SRY-negative XX sex reversal is an autosomal recessive disorder expressed exclusively in XX individuals. Although the mutated gene responsible for the disorder has yet to be identified, further study of the disorder in the American cocker spaniel could lead to the discovery of new genes within the mammalian sex determination pathway. Such studies are currently underway, with the complete canine genome being of significant importance in the identification of associated genes.

As a last note of interest, this particular disorder has been discovered in eighteen other breeds, although it is uncertain if the same gene mutation occurs across all breeds. However, it is suggested that if one is going to buy a female puppy, an androgynous name might be a wise decision.


Posted by Emily Neagle
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References:

Meyers-Wallen, V.N., 2006. Genetics, genomics, and molecular biology of sex determination in small animals. Theriogenology 66-6, 1655-1658. Access Article Here

Kothapalli, K., Kirkness, E., Pujar, S., Van Womer, R., Myers-Wallen, V.N., 2005. Exclusion of Candidate Genes for Canine SRY-Negative XX Sex Reversal. Journal of Heredity 96-7, 759-763.
Access Article Here

OMIA Group. 2004. Sex reversal: XX male (Phene ID 1946, Group 000901) in Canis familiaris. http://omia.angis.org.au/retrieve.shtml?pid=1946. Accessed 25 May 2007