Lecture 23 Evolution And Development Flashcards
Two perspectives on developmental evolution
Phenotypic
genetic
Phenotypic
Adult morphs seen as modifications of timing, rates, and fates of development (quantitative genetics)
Genetic
Reductionist approach, identifying genes responsible for development, led to rethinking homology concepts (population genetics)
Phenotypic examples (3)
Allometry
Isometry
Heterochrony
Allometry
Change in the relative growth of morphological structures, e.g., neoteny, acceleration
Isometry
Uniform growth, no changes in shape (rate is the same through growth)
Heterochrony
Changes in relative timing of developmental events
Mode of developmental changes (2)
Paedomorphosis
Peramorphosis
Paedomorphosis
Gonads mature quickly and a sexually reproductive “juvenile” is produced
Adult looks like juvenile of common ancestor
Progenesis
(early development), truncation of ancestral growth period leads to retention of juvenile characters
neoteny
(slowed development, allometric decrease) reduced rate of development leads to retention of juvenile characters
Paedomorphosis (2)
Progenesis
Neoteny
Peramorphosis
An additional stage is added to the end of developmental sequence (Terminal Addition). A former adult form now becomes a juvenile stage.
Juvenile descendants look like adult of ancestor
Hypermorphosis
(extended development), extensions of ancestral growth period leads to exaggerated adult characters
Acceleration
(allometric increase), increased rate of development leads to exaggerated adult characters
Peramorphosis (2)
Hypermorphosis
Acceleration
Genetic (2)
Homeotic genes and development
Home/Hox genes code for
Transcription factors
Regulatory genes that provide positional information
Hox genes are
Clustered together on chromosomes and their arrangement is highly conserved among animals phyla
Deep homology
Where growth and differentiation are controlled by regulatory genes that are homologous and deeply conserved across a wide range of species even if the subsequent organization and function of those structures is not homologous
Examples of Deep homology “Segmentation/vertebral identity”
Scr, Antp, Ubx expression in arthropods determines main body part boundaries
Hox expression in mice determines number of vertebrae
Example deep homology limbs
“sticky-outeys”
How limbs are made is conserved
Deep homology example eyes
Pax-6, Mammalian gene Pax-6 and the Drosophila gene eyeless are homologous, and both are expressed in developing eyes, despite the fact that the eyes are so different in construction
Pax-6
Can induce eye formation in Drosophila, even on other segments and structures (make eyes)
This a “basic” eye (simple photoreceptor) may have evolved only once, but once that initial structure evolved, improvements in function occurred repeatedly
