Home › Previous year questions › GATE 2020 BT › Question 40GATE 2020 BT – Question 40 Genetics, Cellular and Molecular Biology · Genetics: Mendelian inheritance, gene interaction, complementation, linkage, recombination, chromosome mapping, extrachromosomal inheritance · 2 marks · Multiple choice
A pathway is S → W → X → Y → Z. Four complementation groups of Z-auxotrophs show the following growth on supplementation (Yes = growth):
Mutant | W | X | Y | Z
In order along the four arrows, which groups block the pathway?
Z1, Z2, Z3, Z4 Z4, Z2, Z1, Z3 Z3, Z1, Z2, Z4 Z4, Z1, Z2, Z3 Practise this question in The GATE Grind →
Show answer and explanation Correct answer: (B) Z4, Z2, Z1, Z3
Explanation A supplied intermediate rescues a mutant only if it bypasses that mutant’s blocked reaction. Z4 is rescued by W, so its block precedes W. Z2 first grows on X, so it blocks W→X. Z1 first grows on Y, so it blocks X→Y. Z3 requires the final product Z, so it blocks Y→Z. The arrow order is Z4, Z2, Z1, Z3, B.
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