• Genetic Variation
• Mutations
  • Mutations are random
  • The Lederberg experiment
• Causes of mutations
  • Reviewing DNA
  • Types of mutations
  • Case study: sickle cell anemia
• Gene flow
  • Gene flow: details
• Sex and genetic shuffling
  • Sex and genetic shuffling: details
• Development
  • Types of developmental change
  • Ontogeny and phylogeny
  • Developmental constraints
  • Understanding complexity
  • Hox genes

Development

Development is the process through which an embryo becomes an adult organism and eventually dies. Through development, an organism’s genotype is expressed as a phenotype, exposing genes to the action of natural selection.

Studies of development are important to evolutionary biology for several reasons:

• Explaining major evolutionary change
  Changes in the genes controlling development can have major effects on the morphology of the adult organism. Because these effects are so significant, scientists suspect that changes in developmental genes have helped bring about large-scale evolutionary transformations. Developmental changes may help explain, for example, how some hoofed mammals evolved into ocean-dwellers, how water plants invaded the land, and how small, armored invertebrates evolved wings.

  Mutations in the genes that control fruit fly development can cause major morphology changes, such as two pairs of wings instead of one.		Another developmental gene mutation can cause fruit flies to have legs where the antennae normally are, as shown in the fly on the right.

• Learning about evolutionary history
  An organism’s development may contain clues about its history that biologists can use to build evolutionary trees.

  Characters displayed by embryos such as these may help untangle patterns of relationship among the lineages.

• Limiting evolutionary change
  Developmental processes may constrain evolution, preventing certain characters from evolving in certain lineages. For example, development may help explain why there are no truly six-fingered tetrapods.

	•	Types of developmental change
	•	Ontogeny and phylogeny
	•	Developmental constraints
	•	Understanding complexity
	•	Hox genes

	Lesson plans for teaching about development

• Embryos image after an original by Michael Richardson et al.
• Fruit fly images courtesy of Jean-Michel Muratet, Syndicat National des Ophtalmologistes de France (SNOF).