During embryonic development, the cellular control of limb morphogenesis is governed by a precise balance between cell proliferation (mitosis) and programmed cell death (apoptosis), both regulated by Homeobox (HoxHoxHox) gene products. In a mutant strain of mice, a loss-of-function mutation in the homeobox of the HoxD13 HoxD13\,HoxD13 gene results in syndactyly (fused digits).
Which of the following best explains the molecular and cellular basis of this phenotype?
The mutant HoxD13HoxD13HoxD13 allele causes premature activation of apoptosis in the digital cells, leading to a complete arrest of mitosis and fusion of the remaining structures.
The mutated HoxD13HoxD13HoxD13 protein is unable to bind to DNA as a transcription factor, preventing the activation of genes that trigger apoptosis in the interdigital tissue.
The mutated HoxD13HoxD13HoxD13 protein acts as a direct competitive inhibitor of RNA polymerase II, halting all transcription of genes required for cell survival and mitosis.
The mutant HoxD13HoxD13HoxD13 transcript is incorrectly spliced, leading to a hyperactive protein that continuously stimulates mitosis in both the digital and interdigital zones.
30 exam-style questions on OCR A A Level Biology Cellular control. Each one has a worked solution and a mark scheme showing where the marks go.