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

Step 1 - Understand the Question

The question is about identifying the type of genetic change that influenced the development of the tetrapod limb by altering where a Hox gene is expressed.

Step 2 - Evaluate Each Option

Review each option to see if it fits the description given in the question. (A) Influence of environment on development does not match the context of genetic change. (B) Paedomorphosis involves the retention of juvenile characteristics and does not fit the description of spatial changes. (C) Change in a developmental gene or in its regulation altering spatial organization directly describes a genetic change affecting Hox gene expression and the spatial organization of body parts. (D) Heterochrony refers to changes in the timing of developmental events and not the spatial expression of genes.

Step 3 - Select the Correct Answer

From the evaluation, option (C) is the correct answer, as it accurately describes a change in a developmental gene or its regulation that alters the spatial organization of body parts, fitting the description of the genetic change and Hox gene expression provided in the question.

Key Concepts

Hox genes

Hox genes are a group of related genes that control the body plan of an embryo along the head-tail axis. These genes are highly conserved across many species, meaning they have changed very little throughout evolution.

Hox genes are crucial in determining the identity and positioning of body parts. Each Hox gene is expressed in a specific region of the developing embryo, directing the formation of appropriate structures at specific locations.

For example, if a Hox gene is supposed to form a limb, but is instead expressed in a region that normally forms the tail, this can result in misplaced body parts. This process is tightly regulated to ensure proper development.

A disruption in the regulation of Hox genes can lead to significant changes in an organism's morphology. This can be beneficial, as in the case of tetrapod limb evolution, or harmful, leading to developmental disorders.

Tetrapod limb evolution

The evolution of tetrapod limbs is a fascinating example of how genetic changes can drive significant evolutionary adaptations. Tetrapods include four-limbed animals like amphibians, reptiles, birds, and mammals.

One of the critical steps in the evolution of these limbs was the alteration in the expression of Hox genes. Originally, vertebrate ancestors had fin-like structures. Due to changes in where and when Hox genes were expressed, these fins gradually evolved into more complex limbs with distinct segments like wrists, elbows, and digits.

This transformation did not occur overnight but spanned millions of years. Genetic changes that caused Hox genes to be expressed in new locations within the limb bud were pivotal. These changes enabled the development of new structures that were beneficial for life on land.

Spatial organization of genes

The spatial organization of genes refers to where specific genes are expressed within an organism at various times during its development. This spatial control is crucial for proper development and morphogenesis.

In the context of the exercise, a change in the spatial expression of a Hox gene led to the evolution of tetrapod limbs. Specifically, the gene was expressed along the tip of the limb bud rather than farther back, contributing to the formation of limbs instead of fins.

Regulating the spatial organization of genes ensures that the right structures form at the right locations and times. Misregulation can lead to developmental abnormalities, illustrating the importance of precise control in gene expression and regulation.

Understanding these spatial patterns can help us comprehend how complex body plans and new structures evolve over time, shedding light on the processes that shape the diversity of life we see today.