$W,X$ and $Y$ are the intermediates in a biochemical pathway as shown below:
$$S \cdots \cdots \rightarrow W\rightarrow X\rightarrow Y\rightarrow Z$$
Mutants auxotrophic for $Z$ are found in four different complementation groups, namely $Z1$, $Z2$, $Z3$ and $Z4$. The growth of these mutants on media supplemented with $W$, $X$, $Y$ or $Z$ is shown below (Yes: growth observed ; No: growth not observed):
| Mutants |
Media supplemented with |
| W |
X |
Y |
Z |
| Z1 |
No |
No |
Yes |
Yes |
| Z2 |
No |
Yes |
Yes |
Yes |
| Z3 |
No |
No |
No |
Yes |
| Z4 |
Yes |
Yes |
Yes |
Yes |
What is the order of the four complementation groups in terms of the step they block?
- $S \cdots \cdots \overset{Z1}{\rightarrow}W\overset{Z2}{\rightarrow}X\overset{Z3}{\rightarrow} Y\overset{Z4}{\rightarrow}Z$
- $S \cdots \cdots \overset{Z4}{\rightarrow}W\overset{Z2}{\rightarrow}X\overset{Z1}{\rightarrow} Y\overset{Z3}{\rightarrow}Z$
- $S \cdots \cdots \overset{Z3}{\rightarrow}W\overset{Z1}{\rightarrow}X\overset{Z2}{\rightarrow} Y\overset{Z4}{\rightarrow}Z$
- $S \cdots \cdots \overset{Z4}{\rightarrow}W\overset{Z1}{\rightarrow}X\overset{Z2}{\rightarrow} Y\overset{Z3}{\rightarrow}Z$