The following graph qualitatively represents the gradients of Nodal and Lefty gene products in an early frog embryo. The position along which primary axis is defined by these gradients? Which curves correspond to these two proteins?
A) D-V axis; curves 1 and 2
B) D-V axis; curves 1 and 3
C) A-V axis; curves 1 and 2
D) A-V axis; curves 1 and 3

Question

The following graph qualitatively represents the gradients of Nodal and Lefty gene products in an early frog embryo. The position along which primary axis is defined by these gradients? Which curves correspond to these two proteins? 
A) D-V axis; curves 1 and 2 
B) D-V axis; curves 1 and 3 
C) A-V axis; curves 1 and 2 
D) A-V axis; curves 1 and 3

Quizplus · Accepted Answer

The cells at the vegetal pole secrete two opposing morphogens, Nodal (1) and Lefty (2), the latter being more rapidly diffusing. The result is the domination of Nodal near the vegetal end, and domination of Lefty near the animal end.

The Following Graph Qualitatively Represents the Gradients of Nodal and Lefty