Two intersexual tammar wallabies (Macropus eugenii), one intersexual euro (Macropus robustus) and one intersexual brush possum (Trichosurus vulpecula) were studied.
One tammar had 17 chromosomes instead of the 16 characteristic of the species. There were 14 autosomes and two X and one Y sex chromosomes (XXY intersex). The animal was of female body phenotype (weight basis) and had a pouch containing four everted and well-developed teats with underlying mammary tissue. Undescended non-functional testes were present, one of which was distinctly abnormal. The accessory reproductive structures (apart from the pouch and mammary glands) were of the male type and the penis was well developed.
In the second tammar, dividing cells resembling spermatogonia in one gonad had 14 autosomes and one X chromosome (XO intersex). This animal was of female body phenotype and had a pouch containing two very small teats on one side, with underlying rudimentary mammary tissue. A small scrotum was present. The gonads were nonfunctional, undescended ovo-testes. Both gonads had tissue resembling the interstitial tissue of the normal ovary, and structures containing cells resembling undifferentiated spermatogonia. The accessory reproductive structures were essentially of the female type.
The intersexual euro and the intersexual brush possum (XY intersexes) had well developed pouches containing rudimentary mammae but on dissection were found to have normal male reproductive systems, the testes being within the body cavity. These had small testicular tubules and a greater than normal quantity of interstitial tissue. There were no meiotic stages of spermatogenesis.
It is concluded that the Y chromosome is strongly male-determining and that there is no obvious correlation between karyotype and occurrence of pouch and mammary tissue in marsupials.