Question

You have isolated two temperature-sensitive strains of yeast (which you have named giant and tiny) that show very different responses to elevated temperature. At high temperature, giant cells grow until they become enormous, but no longer divide. By contrast, tiny cells have a very short cell cycle and divide when they are very much smaller than usual. You are amazed to discover that these strains arose by different mutations in the same gene. Based on your understanding of cell cycle regulation, which possibility makes sense?

Group of answer choices

Hyper active Wee1 would generate both tiny and giant strains

Hyperactive form of Cdc25 would generate tiny strain and an inactive form of Cdc25 would generate giant strain

Inactive form of Wee1 would generate giant strain and hyperactive Wee1 would generate tiny strain

Hyperactive Ced25 would generate both tiny and giant strains

Hyperactive form of Cdc25 would generate giant strain and an inactive form of Cdc25 would generate tiny strain

Answer 1

Ans: The correct option is B (Hyperactive form of Cdc25 would generate tiny strain and an inactive form of Cdc25 would generate giant strain).

Under normal circumstances, Wee 1 inactivate Cdk1 by adding phosphate to it and Cdc25 activates Cdk1 by removing phosphate group. Mutation in Wee 1 and Cdc25 may produce giant and tiny temperature-sensitive yeast strains.
A mutation in the Cdk1 gene that produces an inactive protein will arrest the cell cycle and lead to the production of giant cell. A mutation that arrests the inactivation of Cdk1 gene by Wee 1 lead to the production of tiny cell that will show cell division continuously.

By keeping above mentioned reasoning in mind, it could be interpreted that hyperactive Wee 1 will inactivate Cdk1 gene and lead produce giant cell and inactive Wee 1(or hyperactive Cdc25) will leave Cdk1 gene permanently active, leading to the production of tiny cells.