Question

John Gurdon performed nuclear transplant experiments in frogs to test two different hypotheses to explain why specialized cells become restricted in their fates during development. His results supported the hypothesis that differentiation involves genome regulation, where unneeded genes are progressively turned off, but are not lost from the genome of cells as they differentiate. However, Gurdon's results showed that only 10 out of 726 eggs that received transplanted nuclei from mature cells differentiated into tadpoles, whereas 716 did not. Why did Gurdon use these rare successful nuclear transplantations as evidence for the gene regulation hypothesis?

a. If the gene regulation hypothesis was wrong, and genes were lost from the genome during development, the eggs would have been able to differentiate into ectoderm and mesoderm, but not endoderm cells from which the nuclei originated.

b. If the gene regulation hypothesis was wrong, and genes were lost from the genome during development, all of the eggs would have been able to differentiate into tadpoles.

c. If the gene regulation hypothesis was wrong, and genes were lost from the genome during development, none of the eggs would have been able to differentiate into tadpoles.

Answer 1

John Gurdon's experiments supported the gene regulation hypothesis by showing that successfully developed tadpoles from transplanted nuclei demonstrate that specialized cells retain their entire genome during differentiation, rather than losing genes.

Step-by-step explanation:

John Gurdon used the successful nuclear transplantations in frogs as evidence for the gene regulation hypothesis because it demonstrated that specialized cells retain all their genetic information despite differentiation. According to this hypothesis, during development, cells turn off genes that are not needed but do not lose these genes from the genome.

The successful development of tadpoles from eggs that received transplanted nuclei proves that differentiation involves the regulation of genes, not the loss of genes. Hence, even if the success rate was low (10 out of 726), the fact that any tadpoles developed at all was a significant support for gene regulation. If the genes had been lost, as the alternative hypothesis suggested, none of the eggs would have had the necessary genetic information to develop into tadpoles.