The \"snout\" of a frog tadpole bears a sucker. A salamander tadpole has a musta

Question

The "snout" of a frog tadpole bears a sucker. A salamander tadpole has a mustache-shaped structure called a balancer in the same area. Suppose that you perform an experiment in which you transplant ectoderm from the side of a young salamander embryo to the snout of a frog embryo. The tadpole that develops has a balancer. When you transplant ectoderm from the side of a slightly older salamander embryo to the snout of a frog embryo, the frog tadpole ends up with a patch of salamander skin on its snout. Suggest a hypothesis to explain these results in terms of developmental mechanisms. How might you test your hypothesis?

Explanation / Answer

In the given case, transplantation was performed at two different stages of development:

Case I – Embryo stage: Transplanting ectoderm from salamander embryo to frog embryo has resulted in the tadpole with balancer.

Case II – Adult stage: Transplanting ectoderm from old embryo salamander to old embryo frog has resulted in the tadpole with patch of salamander skin.

The difference in above results is due to different stages of differentiation. In case I, no differentiation of ectoderm occurred resulting in formation of balancer in the frog.

In case II, transplant was taken from old embryo which have already differentiated ectoderm. During differentiation of ectoderm, three components of the ectoderm will give rise to a particular set of cells.

Hence, it can be hypothesized that transplant is taken from epidermal cell region which resulted in formation of salamander skin patch in frog.

Following Hypothesis experiments can be planned to verify the above assumption:

Set 1: Control: No transplantation

Result: No balancer in frog          

Set 2: Transplantation of ectoderm from young salamander embryo to young frog embryo

Result: Balancer in frog

Set 3: Transplantation of ectoderm from old salamander embryo to old frog embryo

Result: Skin patch in frog             

Set 4: Expose the ectoderm Transplant of young salamander embryo with chemicals that promote differentiation and subsequently perform transplantation in young frog embryo.

Result: Skin patch in frog

As results of Set 4 produce a skin patch in frog, it indicates the only undifferentiated ectoderm is capable to form a balancer.

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