Problem 6 - Campbell Biology

Question

A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of (A) the influence of environment on development. (B) paedomorphosis. (C) a change in a developmental gene or in its regulation that altered the spatial organization of body parts. (D) heterochrony.

Step-by-Step Solution

Answer

(C) a change in a developmental gene or in its regulation that altered the spatial organization of body parts.

Step 1 - Understand the Question

The question asks about the type of genetic change that led to the evolution of the tetrapod limb due to a Hox gene expression shift.

Step 2 - Identify Key Information

Focus on the key terms: Hox gene, expression shift, vertebrate limb bud, and evolution of the tetrapod limb. Recall that Hox genes are crucial in determining the spatial organization of body parts during development.

Step 3 - Review Answer Choices

Consider each choice: (A) the influence of environment on development, (B) paedomorphosis, (C) a change in a developmental gene or in its regulation that altered the spatial organization of body parts, and (D) heterochrony.

Step 4 - Analyze Each Answer Choice

Analyze and eliminate incorrect options: - (A) The influence of the environment on development is not directly related to a genetic change in a Hox gene.- (B) Paedomorphosis refers to the retention of juvenile features in the adult organism, which is not relevant here.- (D) Heterochrony deals with changes in the timing of developmental events, not the spatial organization of body parts.

Step 5 - Select the Correct Answer

The correct choice is (C) a change in a developmental gene or in its regulation that altered the spatial organization of body parts, as this directly relates to the shift in Hox gene expression affecting limb development.

Key Concepts

Hox gene

Hox genes are a group of related genes that play a crucial role in determining the basic structure and orientation of an organism's body. They are a type of developmental gene that guides the spatial organization of body parts in developing embryos. These genes are like the body's blueprint architects. They tell the cells in different regions what structures to form. For example, Hox genes ensure that arms, legs, and head grow in the correct places on the body. Mutations or changes in the expression of Hox genes can lead to significant changes in an organism's body plan. In the case of tetrapods, a change in Hox gene expression was key to the development of limbs instead of fins.

developmental gene regulation

Developmental gene regulation involves the control of gene expression during an organism's development. It's about turning genes on and off at the right times and places to form the unique parts of a body. Imagine a construction manager deciding when to build different parts of a house. Similarly, regulatory mechanisms ensure that specific Hox genes are active only where and when needed. This precise control is vital for normal development. For example, in limb development, specific Hox genes must be activated in the limb bud to guide the formation of limbs. Disruptions in this regulation can lead to developmental anomalies or evolutionary changes. In tetrapod evolution, a regulatory change in Hox gene expression led to limbs instead of fins.

spatial organization of body parts

The spatial organization of body parts refers to the specific arrangement and placement of structures in an organism. Hox genes are fundamental in organizing this spatial layout during embryonic development. They ensure that body parts grow in the correct positions and proportions. This organization follows a specific sequence along the body's axes, like head to tail. For instance, in vertebrates, the correct spatial expression of Hox genes ensures limbs like arms and legs develop in precise locations. A shift in Hox gene expression can alter this organization, potentially changing the body plan. The evolution of tetrapod limbs from fish fins is a prime example of changes in spatial organization driven by genetic changes.

tetrapod evolution

Tetrapod evolution is the process through which four-limbed vertebrates emerged from their fish ancestors around 360 million years ago. This transition involved significant changes in body plan, particularly in the development of limbs. Key to this transformation was the alteration in the expression of Hox genes. These changes allowed for the development of distinct limb structures such as arms and legs, facilitating life on land. The movement from a water-based environment to land required new adaptations, including stronger limb bones and joints for support and mobility. The genetic shift in Hox genes exemplifies how evolutionary changes can start at the microscopic level, resulting in significant morphological innovations.