Evolution of Morphology

Question 1

What is the tremendous increase in diversity during the Cambrian seen as?

Answer 1

It is a puzzle
- Could changes in genes that are involved in development result in new morphological forms?

Question 2

‘Evo-Devo’

Answer 2

The study of evolutionary developmental biology
- Developmental is the process that gives rise to form, and so the evolution of form is brought about through the evolution of development
- Genes that program development control the rate, timing, and spatial pattern of changes in an organism’s form as it develops to adulthood
- Studying genetic mechanisms of change can provide insight into large-scale macro-evolutionary patterns

Question 3

What is a basic genetic ‘toolkit’?

Answer 3

• The genes responsible for building bodies and body parts
• Shared by virtually all animals
• Many animal ‘toolkit’ proteins exhibit functionally equivalent activity in vivo when substituted for one another

Question 4

How does morphological diversity evolve?

Answer 4

Consider a species that exists in different forms, the forms can be more distinct in terms of morphology and ecology than the adult forms of any pair of sister species

Question 5

The Genetic Theory of Morphological Evolution

Answer 5

• Proposed by Sean Carroll of U. of Wisconsin
• Form evolves largely by altering the expression of functionally conserved proteins
• Such changes largely occur through mutations in the promoter sequences of the regulatory genes and their target genes that participate in developmental pathways

Question 6

Transcription factor

Answer 6

A protein that binds to specific sequences of DNA (the Cis-regulatory elements) to control the transcription of genetic information from DNA to RNA
- Specific transcription factors bind to specific regulatory control regions in the promoter

Question 7

What does the genetic theory of morphological evolution propose?

Answer 7

That gain, loss, or modification of sequences in these promoter and other regulatory control regions of genes is the predominant mechanism underlying evolution of development and form

Question 8

What gene is involved in limb formation?

Answer 8

The gene Prx1
- Scientists replaced the promoter of the mouse Prx1 gene with the promoter of the fruit bat Prx1 gene
- Promoters shared 94% similarity
- Resulting mice had longer limbs than usual
- Suggests that bat wings may have arisen through changes in promoter sequence

Question 9

Changes in gene sequence

Answer 9

• New morphological fors may also arise from mutations within the coding sequence of developmental genes
• A possible mechanism for the evolution of six-legged insects from a many-legged crustacean ancestor has been demonstrated in lab experiments
• Specific changes in the Ubx gene have been identified that can “turn off” leg development