Question

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.

Short answer

The strongest evidence for the conservation of tool-kit genes is provided by option (c), where a mouse Hox gene can be used to take over the function of a mutated Drosophila Hox gene. This example demonstrates the conservation and functionality of Hox genes across different species.

Step-by-step solution

Understanding tool-kit genes

Tool-kit genes are a set of genes that are essential for the development of organisms. They are highly conserved across different species, meaning they have remained relatively unchanged throughout evolution due to their crucial role in the development process.

Evaluating Option a

In this scenario, the bicoid gene is moved from one fly embryo into another fly embryo, which results in the formation of two head regions. It does show that the bicoid gene has a significant role in the development of the organism, but it does not demonstrate conservation across different species.

Evaluating Option b

Here, a mutation in an unrelated gene in another species of fly has a similar effect as a mutation in the bicoid gene in Drosophila. This information does not provide evidence for the conservation of tool-kit genes because it involves an unrelated gene and does not show any effect of a conserved gene being utilized across different species.

Evaluating Option c

This option states that a mouse Hox gene can take over the function of a mutated Drosophila Hox gene. This is an example of a conserved tool-kit gene (Hox genes) functioning across different species (mice and Drosophila). Thus, it provides strong evidence for the conservation of tool-kit genes.

Evaluating Option d

The cloning of sheep by fusing a differentiated adult cell with an enucleated egg is an interesting example of genetic manipulation, but it does not provide evidence for the conservation of tool-kit genes across different species.

Answer

Therefore, the strongest evidence for the conservation of tool-kit genes is provided by option (c), where a mouse Hox gene can be used to take over the function of a mutated Drosophila Hox gene. This example demonstrates the conservation and functionality of Hox genes across different species.

Key concepts

Hox Genes

Hox genes are a fascinating class of genes crucial for determining the body plan of an organism during early developmental stages. Found in clusters on chromosomes, Hox genes dictate the head-to-tail body layout, ensuring that body parts develop in the correct order. The unique characteristic of Hox genes is their collinear arrangement, where the physical location of a Hox gene on a chromosome corresponds to its area of influence in the body.
For example, if a specific Hox gene is located at the beginning of the cluster, it might control the development of the head region. As we progress along the chromosome, genes control posterior body regions. This precise coordination is vital for proper organismal development, highlighting the importance of Hox genes in developmental biology.

Gene Conservation

Gene conservation refers to the stability of genes across different species over evolutionary time. Certain genes, like Hox genes, are crucial for basic biological functions and therefore remain relatively unchanged, or conserved, throughout evolution. These genes provide essential roles in development and survival, which explains their high level of similarity across diverse organisms.
Why is gene conservation important?

• Provides insights into the evolutionary relationships between species.
• Highlights essential biological processes preserved over millions of years.
• Offers potential for cross-species scientific and medical research.

The high level of conservation of tool-kit genes emphasizes their fundamental role across species, demonstrating the minimal changes needed for species survival and reproduction through the ages.

Developmental Biology

Developmental biology is the study of the processes by which organisms grow and develop. One core aspect of developmental biology is understanding how genes like the Hox genes contribute to the regulation of developmental processes. These genes control the spatial and temporal expression of various proteins that lead to the formation of tissues and organs.
Through developmental biology, we learn how:

• Organisms transform from single cells into complex multicellular entities.
• Specific genes regulate developmental pathways.
• The process ensures accuracy in species-specific body structures.

Detailed knowledge of developmental biology helps identify why certain genetic disorders occur and can assist in developing genetic therapies to rectify these anomalies.

Cross-Species Gene Functionality

Cross-species gene functionality refers to the ability of genes from different species to perform similar or identical roles. This is evident in instances where genes from one species are introduced into another, yet they perform their expected biological functions. Such functionality indicates high conservation and similarity of genetic mechanisms across species.
For example, a Hox gene from a mouse can fulfill the role of a defective Drosophila Hox gene, showcasing the conserved nature of their functions despite being different organisms. This phenomenon is crucial for scientific research, as it allows genes to be studied in various models and provides understanding in:

• The fundamental genetic architecture of species.
• The potential for transgenic and genetic therapy applications.
• The evolutionary conservation of life’s critical genetic blueprints.

By leveraging cross-species gene functionality, scientists can harness genetic information from model organisms to advance human health and medicine.