Gender:  In the Genes or in the Jeans?

The Y chromosome directs differentiation of gonads in the male direction. Is this chromosome responsible for the other levels of sexual differentiation you came up with in Part I? Let’s look next at the differentiation of male and female ducts.

The gonads are connected to the outside world by a system of ducts through which the gametes may travel. In the very young embryo, there are actually two sets of ducts present, called Mullerian and Wolffian after their discoverers. As the fetus develops, one set disintegrates while the other develops into the duct system appropriate for that sex.

In females, the Wolffian ducts disintegrate and the Mullerian ducts develop to become the oviduct, uterus, and the upper part of the vaginal canal. In males, Mullerian ducts disintegrate and the Wolffian ducts develop to become the vas deferens, epididymis, and seminal vesicles.

These changes occur when the gonad is developing, so scientists wondered if the Y chromosome itself doesn’t determine duct differentiation, but rather something from the gonad causes the appropriate ducts to develop. The following set of experiments was conducted to find out.

Questions

1. Does the female gonad secrete something that causes the Mullerian ducts to develop and Wolffian ducts to disintegrate? The ovaries were removed from a group of female rats during early fetal development. After birth, these females and normal females were examined to see which ducts developed. (A + indicates that this duct did develop, a - indicates that it disintegrated.)
    

   Experiment	Mullerian	Wolffian
   Normal female	+	-
   Remove ovaries	+	-

   
   What would you conclude about the role of the ovary in causing differentiation of the ducts in females?
    
    
2. Does the male gonad secrete something that affects male differentiation? In this experiment, the testes were removed from a developing fetus and the subsequent development of the ducts was noted as follows:
    

   Experiment	Mullerian	Wolffian
   Normal male	-	+
   Remove testes	+	-

   
   What would you conclude now about the role of the testes in causing differentiation of the ducts in males?
    
    
3. The testes secrete testosterone. Is this hormone responsible for Wolffian duct development and Mullerian duct disintegration? In one experiment, scientists removed the testes and injected testosterone into the male fetuses. In another experiment, they used normal males with their testes intact and into these animals they injected a drug that has an anti-testosterone effect, that is, it prevents testosterone from acting. Here are the results:
    

   Experiment	Mullerian	Wolffian
   Normal male	-	+
   Remove testes	+	-
   Remove testes and inject testosterone	+	+
   Intact male + anti-testosterone	-	-

   
   What would you conclude now about the role of testosterone in differentiation of the male ducts?
    
    
4. Let’s look at one more experiment on a male fetus. In this case the experimental manipulation was to remove the gonad from one side only. The results are presented below:
    

   Experiment	Mullerian	Wolffian
   Normal male	-	+
   Remove testes	+	-
   Remove left testis only and observe left side	+	+
   Remove left testis only and observe right side	-	+

   
   What would you conclude now about the role of the testes in differentiation of the male ducts?
    
    
5. Fill in your flowchart to indicate the differentiation of the Wolffian and Mullerian ducts.

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