Which of the following provides the strongest evidence for the conservation of tool-kit genes? a. Bicoid moved from one fly embryo into the posterior of another fly embryo causes the formation of two head regions. b. Mutation of an unrelated gene in another species of fly has a similar effect to mutation of bicoid in Drosophila. c. A mouse Hox gene can be used to take over the function of a mutated Drosophila Hox gene. d. Sheep can be cloned by fusing a differentiated adult cell with an enucleated egg.

Verified step by step guidance

1. Identify the concept of 'tool-kit genes': Tool-kit genes are a set of genes that are conserved across different species and are fundamental in controlling key processes in development, such as body plan layout.
2. Analyze option a: This option shows that bicoid, a gene known for its role in head development in flies, can induce a similar developmental process in a different part of an embryo when moved. This suggests a specific, conserved role for bicoid in head formation.
3. Analyze option b: While this option indicates a similarity in gene function across species, it does not directly demonstrate the conservation of the same gene, but rather a similar phenotype resulting from mutations in potentially different genes.
4. Analyze option c: This option directly supports the concept of tool-kit genes by demonstrating that a gene from a mouse (a different species) can replace and perform the function of a similar gene in Drosophila. This indicates a strong conservation of gene function across species.
5. Analyze option d: This option involves cloning and the use of differentiated cells, but does not directly relate to the conservation of specific developmental genes across different species.