ch 23: Natural Selection Flashcards
The current theory about how life arose consists of four main stages
- Small organic molecules were synthesized.
- These small molecules joined into macromolecules, such as proteins
- All these molecules were packaged into protocells, membranes containing droplets, whose internal chemistry differed from that of the external environment.
- Self-replicating molecules emerged that made inheritance possible.
Earth formed since …
4.6 Billion years ago, Because of the heat from the bombardment of rock left over from the formation of the universe any water available was vaporized and seas were prevented from forming.
What happened after rocks bombarded
When this slowed The atmosphere was theorized to be composed of water vapor, nitrogen, oxides, CO2, CH4, Ammonia, Hydrogen, and Hydrogen sulfides. (volcanos)
What happened as the earth cooled
As the earth cooled the water condescended and oceans formed much of the hydrogen escaped into space
When did life arise
Life emerged 3.8 to 3.9 Billion years ago (first ¾ Earth’s history all life was microscopic and primarily unicellular.) Prokaryotes fossils 3.5 Billion years ago
Oparin and Haldane
independently hypothesized that the atmosphere was a reducing environment.
What 2 steps were taken by Oparin and Haldane
- Powered by lightning and intense UV radiation
2. This reducing environment could cause organic synthesis
Miller and Urey
Test this hypothesis and produced a variety of amino acids.
However, the evidence is not yet convincing that the early atmosphere was in fact reducing
Miller-Urey–type experiments demonstrate that organic molecules could have formed with various possible atmospheres
instead in Miller and Urey experiment
Instead of forming in the atmosphere, the first organic compounds may have been synthesized near volcanoes or deep-sea vents
what was the first genetic mat
It is hypothesized that self-replicating (auto-catalytic) RNA (not DNA) was the first genetic material.
RNA
- Plays a central role in protein synthesis
2. Can also act as an enzyme
Relative dating
using the order of rock strata to determine the relative age of fossils.
Radiometric dating
using the decay of radioactive isotopes to determine the age of the rocks or fossils. Based on the Half-life (rate of decay) of isotopes.
The earliest living organisms were
prokaryotes
About 2.7 Billion years ago
Oxygen began to accumulate because of photosynthesis
2.1 bya
eukaryotes appeared
Endosymbiotic Hypothesis
mitochondria and plastids (chloroplast) were formerly small prokaryotes that began living within larger cells
Evidence for Endosymbiosis
- Both organelles have enzymes and transport systems homologous to those found in the plasma membrane of living prokaryotes
- Both Replicate by splitting process similar to prokaryotes
- Both contain single, circular DNA molecules, not associated with histone proteins
- Both have their own ribosomes which can translate their DNA into proteins.
3 rando facts
- Continental drift helps explain the disjunct geographic distribution of certain species
- Fossil freshwater reptiles is found in both Brazil and Ghana (West Africa)
- Also why no eutherian (placental) mammals are indigenous to Australia
MASS EXTINCTIONS(4)
- The fossil record shows that most species that have ever lived are now extinct
- Extinction can be caused by changes to a species’ environment
- At times, the rate of extinction has increased dramatically and caused a mass extinction’
- Mass extinction is the result of disruptive global environmental changes
In each of the five mass extinction events
more than 50% of Earth’s species became extinct
The last one 65 mya
lost the dinosaurs
ADAPTIVE RADIATIONS
- Adaptive radiation is the evolution of diversely adapted species from a common ancestor
- Adaptive radiations may follow’
- Mass extinctions
- The evolution of novel characteristics
- The colonization of new regions
Substantial evolutionary change
the result from alterations in genes that control the placement and organization of body parts
Homeotic genes
determine such basic features as where wings and legs will develop on a bird or how a flower’s parts are arranged
Hox genes
are a class of homeotic genes that provide positional information during development
If Hox genes are expressed in the wrong location, body parts can be produced in the wrong location
For example, in crustaceans, a swimming appendage can be produced instead of a feeding appendage
New morphological forms come from
duplication events that produce new 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
Changes in morphology likely result
from changes in the regulation of developmental genes rather than changes in the sequence of developmental genes
For example, threespine sticklebacks in lakes have fewer spines than their marine relatives
The gene sequence remains the same, but the regulation of gene expression is different in the two groups of fish
cool
CHANGES IN RATE AND TIMING’
Heterochrony is an evolutionary change in the rate or timing of developmental events
- It can have a significant impact on body shape
- The contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates
- Heterochrony can alter the timing of reproductive development relative to the development of nonreproductive organs
- In paedomorphosis, the rate of reproductive development accelerates compared with somatic development
- The sexually mature species may retain body features that were juvenile structures in an ancestral species
