Marsupials

Question 1

Describe the features of marsupials

Answer 1

• Chromosomal sex determining mechanism
• Males → scrotum, testis and bifurcated penis
• Females → pouches and mammary glands
• Marsupial offspring very small at birth (12-750mg)
• Pregnancy lasts 28 days, all organogenesis occurs in the last part
• Newborns exhibit negative geotropism to migrate to pouch
• Maternal hormones such as prostaglandins simulate the mother to adop a posture that makes it easier for the offspring to navigate north to the pouch
• Newborn joey has enough energy to make the journey from the urogenital sinus to the pouch twice
• Offpsring will attach to the mammary gland in the pouch

Question 2

Phenotypic Characteristics of Intersex Marsupials

Answer 2

XO- Turners equivalent
• Ovaries are streak gonads (XO germ cells cant survive)
• Mullferian ducts present
• Wolffian ducts absent
• No penis
• Scrotum present (only difference to human turners)

XXY – Klinefelters equivalent
•	Intraabominal testis
•	Mullerian ducts absent
•	Wolffian ducts present
•	Penis developed
•	Pouch and mammary gland (different to human)
•	No scrotum (different to human)

• Must therefore be genes on the X which are responsible for development of female pouch and mammary tissue
• Could be X dose dependent:
• One X → no pouch, but a scrotum
• Two X → pouch and mammary gland
• Normal XY males → no pouch or mammary gland. No male marsupial is known to produce breast tissue (in contrast with mammals – Klinefelters, Testicular Feminisation, X linked suppressor of SRY)
• Marsupials – mammary gland development chromosomally mediated
• Eutherians – estrogen is the switch