In this chapter, we have focused on large-scale as well as the inter- and intracellular events that take place during embryogenesis and the formation of adult structures. In particular, we discussed how the adult body plan is laid down by a cascade of gene expression, and the role of cell–cell communication in development. Based on your knowledge of these topics, answer several fundamental questions:

How did we discover that selector genes specify which adult structures will be formed by body segments?

Key Concepts

Selector Genes

Selector genes are a group of regulatory genes that determine the identity of body segments during embryonic development. They function by activating specific developmental pathways that lead to the formation of distinct structures in the adult organism. The discovery of their role was largely facilitated by genetic studies in model organisms, such as Drosophila, where mutations in these genes resulted in the transformation of one body segment into another.

Gene Expression Cascade

A gene expression cascade refers to a series of sequential gene activations that lead to the development of specific traits or structures. In embryogenesis, this cascade is crucial for establishing the body plan, as it orchestrates the timing and spatial distribution of gene activity. Understanding this cascade helps explain how complex organisms develop from a single fertilized egg into a fully formed adult.

Cell–Cell Communication

Cell–cell communication is essential for coordinating developmental processes during embryogenesis. It involves signaling molecules that allow cells to communicate their position and developmental status to neighboring cells, influencing their fate. This interaction is vital for ensuring that the correct structures form in the right locations, as it helps integrate the activities of selector genes and the gene expression cascade.