chapter 19 part 2 Flashcards
Describe how homology and novel characteristics can work together
Novel characteristics: include both new modifications of ancestral structures, such as the elongated incisors that are tusks of an elephant, and what may be considered truly new structures
Result from formation of new or greatly altered gene interaction networks
Can happen possibly from many differences in gene regulation
Biological Homology
similarity of repeated structures within an organism, and of structures in different species, suggest that are based on a similar genetic developmental program
Occurs in two species if their common ancestor did not express the feature
Sometimes lost features are regained
Deep homology
genetic regulatory pathways that may be widely inherited and indendpently expressed in distantly related lineages and may contribute to remarkable different features
Describe the relationship of deep homology and Distal-less
Suggest that the same genetic input (Distal-less for example) can support a common developmental basis for diverse features in different lineages
Example: genetic pathway governed by Distal-less gene is the basis for very different structures in distantly related animals
Example: genetic network that includes Distal-less gene triggers outgrowths during development of starfish and insects
Describe the relationship between Pax-6 gene and Deep homology
Example: homologues of Pax-6 gene intitate the development of eyes in arthrorpods, vertebrates, and other animals, and the same genetic signaling networks (Bmp, Wnt, and others) govern limb development in vertebrates and arthropods, and even the tentacles of squids
Explain the relationship of deep homology amongst verts and inverts
despite the different structures of vertebrae and arthropod legs and squid or octopus tentacles, they evidently share a similar gene network
Similar earlier expression in six key genes
Developmental systems drift
genetic and developmental base of phylogenetic homologous features, uncommon I think
Show that a trait may stay much the same despire variable genetic input into its development
Name an example of developmental systems drift
Example: in all tetrapod vertebrates, the differentiation of the digits is based on the action of Shh and Bmp genes
Digits differentiated from back (pinky) to front (thumb) except in salamanders, which have front-to-back differentiation
What is rate of evolution?
o Rate of evolutionary change (change per unit time) varies greatly among characters, among evolving lineages, and within the same lineage over time
How long does short-term evolutionary change take to make net change?
about 1my, after that substantial
Example: horses increasing by factor of 10 after 25my
What are the possible explanations to why evolution is often so slow?
Conservatism (like among mammals in 7 neck vertebrate and limb bones, so many traits still the same or quite similar across groups like vertebrates)
Extreme cases are living fossils (coelocanths ex)
Phylogenetic niche conservatism
species long-continued dependence on much of the same resources and environmental conditions
Slow evolution of the ecological requirements of a group of organisms, results in this
anagenesis
evolutionary change within a single species lineage
Cladogenesis
branching lineages into different species
hypothesis of punctuated equilibria
Most evolutionary change has occurred not gradually and incrementally over the course of long time spans but rather in newly formed species that originate by peripatric speciation
NOT widely accepted, but speciation might increase rate of character evolution for other reasons
What are other reasons for increasing the rate of character evolution for speciation?
- Enables evolutionary changes to persist long term
- Few character changes amongst wide spread ranges of a population could be advanteageous; species seldom evolve as a unified whole
What does speciation often require?
often entails both reproductive isolation and ecological divergence
What are the two models of phenotypic evolution?
phyletic gradualism (the famililar one) and punctuated equilibria (substantial pehnotypic change happens only during speciation events)
