Developmental Biology and Evolution

佟超浙江大学生命科学研究院

Outline

• Overview• Preconditions for evolution• Deep homology• Mechanisms of evolutionary changes• Developmental constrains on evolution• Selectable epigenetic variation• Summary

What is Evolution ?

What is Evolution ?

Evolution is the change in the inherited characteristics

of biological populations over successive generations. Evolutionary processes give rise to diversity at every level of biological organization, including species, individual organisms and molecules such as DNA and proteins.

• Descent from a common ancestor

• Natural selection

• At the different level

What is Evolution ?

Timeline of evolution theory

1735 biological classification

1809Lamarckism

18580n the origin of species

1865Mendel's laws

1896Weismannism“germ cells vsSomatic cells”

population genetics

1953DNA structure

Galapagos

Summary of Darwin’s theory

Every species is fertile enough that if all offspring survived to reproduce the population would grow (fact).

Despite periodic fluctuations, populations remain roughly the same size (fact).

Resources such as food are limited and are relatively stable over time (fact).A struggle for survival ensues (inference).

Individuals in a population vary significantly from one another (fact).Much of this variation is inheritable (fact).

Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their inheritable traits to future generations, which produces the process of natural selection (inference).

This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species (inference).

Ernst Mayr 

Why we need to understand evolution?

"nothing in biology makes sense except in the light of evolution"

Theodosius Dobzhansky

Basics of Biology

• Theory of evolution

• Mendelian inheritance

• The central dogma of molecular biology

How “far” away they are

How “close” they are

How does evolution work

• Preconditions for evolution: The developmental structure of genome

• Modularity• Molecular parsimony The small tool kit

Modularity: Divergence through dissociation

Modularity: Divergence through dissociation

• Apterous

Molecular parsimony: gene duplication and divergence

• Some “tool kit” genes play the same roles in all animals

• Gene duplication provides opportunities for divergence.

• Paralogues• Orthologues

Molecular parsimony: gene duplication and divergence

Deep Homology

Mechanisms of evolutionary change

Evolution works with what it has:

• Change in location (Heterotopy)• Change in time (Heterchrony)• Change in amount (Heterometry)• Change in kind (Heterotypy)

Heterotopy

Fgf8

BMP

apoptosis

Heterotopy

Fgf10 attract ribs to enter the dermis

BMP induce the bone formation

Heterchrony

Heterometry

• Darwin’s finches

Heterometry

Heterotypy• Why insects have only six legs?

Developmental constraints on Evolution

• Physical constraints

• Morphogenetic constraints

• Phyletic constraints

Physical constraints

Morphogenetic constraints

Phyletic constraints

Selectable epigenetic variation:Environment cues

• Somatic cells VS germ cells What is wrong with lamarck?• Epialleles• Symbiont variation• Genetic assimilation

Epialleles

Symbiont variation

Interaction with an expected population of symbionts could result in phenotypic plasticity.

When symbionts are transmitted through the germ line, the symbionts provide a second system of inheritance.

Symbiont variation

Genetic assimilation

• The environment could both “induce” and “select” a phenotype.

• Genetic assimilation happens both in labs and in nature.

• Fixation of environment induced phenotypes 1. The phenotype is not random. 2. The phenotype already exists in a large

portion of population

Summary• Variation-modularity, molecular parsimony, and

duplication- enable changes in development without destroy the organism.

• Four modes of genetic changes act during development to produce new and large variation in morphology.

• Epigenetic inheritance provide selectable variations and aid their propagation through a population.