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.

Verified step by step guidance

1. Identify the key concept: The question describes a genetic change affecting the expression of a Hox gene, which influences the development of limb structures in vertebrates.
2. Understand the role of Hox genes: Hox genes are crucial in determining the body plan and the positioning of various structures during embryonic development. They control the anterior-posterior axis formation and help differentiate the types of structures that will form at specific locations.
3. Analyze the options: Option (c) mentions a change in a developmental gene or its regulation that altered the spatial organization of body parts, which directly relates to the role of Hox genes in determining where limbs and other structures develop.
4. Eliminate unrelated options: Options (a), (b), and (d) do not directly address changes in gene expression affecting spatial organization. Option (a) involves environmental influence, option (b) involves retaining juvenile features in adults, and option (d) involves timing changes in developmental processes.
5. Conclude with the correct answer: Based on the role of Hox genes in spatial organization during development, the correct answer is (c) a change in a developmental gene or in its regulation that altered the spatial organization of body parts.

Key Concepts

Hox Genes

Hox genes are a group of related genes that determine the body plan of an embryo along the anterior-posterior axis. They play a crucial role in the development of structures such as limbs and organs by regulating the expression of other genes. Changes in Hox gene expression can lead to significant morphological variations, as seen in the evolution of tetrapod limbs.

Developmental Gene Regulation

Developmental gene regulation refers to the mechanisms that control the timing, location, and amount of gene expression during development. Alterations in these regulatory processes can lead to changes in the spatial organization of body parts, influencing the overall morphology of an organism. This concept is essential for understanding how genetic changes can result in evolutionary adaptations.

Heterochrony

Heterochrony is the term used to describe changes in the timing of developmental events, which can lead to variations in size and shape among organisms. It can result in paedomorphosis, where juvenile traits are retained in adults, or peramorphosis, where adult traits are exaggerated. Understanding heterochrony is vital for explaining how evolutionary changes can occur through shifts in developmental timing.