Evolution Lecture 7 Flashcards
Fossils
Preserved remnants (or traces) of past life in rock. Some examples are:
– Mineral components
– Petrified organic material
– Casts
– Trace fossils (footprints etc)
It tells us information about past ecosystems; climate;
sea levels etc., & dating of geological record. More direct view of evolutionary history than from living organisms. They are biased for species the existed for a long time.
Sedimentary Rock
Where most fossils are found. They are found in the bottom of lakes, layers keep adding show a passage of time. Where mineral particles fall into the water bodies then form layers (other dead animals can get trapped here then are in the rock before they fully decay). They then get compared by heat into solid rock over many years.
Why is the sedimentary rock slanted?
Because it’s very very old.
Where can fossils also be found?
Frozen in ice or in amber (tree sap).
Strata
Sedimentary rock layers.
Archaeopteryx
Fossil of a dinosaur with feathers seen in it. It’s an articulated fossil because it’s all intact.
Index Fossil
Common, widespread fossils characteristic of particular periods of earth’s history. Crucial for ‘relative dating’ in geological record. Eg. shells of single cell organisms.
What can we find out about extinct things from extinct?
Their biology and age.
The geological record
The fossil record is in this. There is a relationship between them. Earth is ~4.6 billion years old. (Microbial) life arose ~3.5+ billion years ago. Fossils of animals & plants common in the last ~550 million years: “Phanerozoic Eon.”
Phanerozoic divided into three what?
Eras
Each Era subdivided into several what?
Periods
The three Eras in order?
Paleozoic, Mesozoic, Cenozotic. This is the last 15% of earths time.
When were the eras worked out?
In the 19th century using many different dating methods, such as index fossils. 20th century use radioactive decay allowed to be sure if date rocks.
Radioactive Decay
Radioactive parent isotope decay to a daughter isotope at a charcuterie rate.
Half-life
the time required for 50% of the parent isotope to decay.
Periods
Subdivisions of eras. They aren’t the same length.
How did the period change occur?
Saw a sudden change in the geological record, where the fossils in rocks changed into different rocks. (the eras change is the same but with bigger differences).
Mass extinctions
Many species extinct in very short time. Causes: large environmental changes. Plausible examples:
– Massive volcanic activity
– Impact by asteroid or comet
Major importance in history of life. Extinction occur all of the time. Only the survivors can speciate.
How many mass extinction are there?
5 big ones, most marking ends of Eras/Periods.
End-Permian mass extinction
~250 million years ago. Most devastating mass extinction. Extinction of ~90% of species on earth. Many large taxa went totally extinct (e.g. ~50% of Families). Guessed that it was caused by volcanoes.
End-Cretaceous mass extinction
~65 million years ago. Most recent ‘big’ mass-extinction. Extinction of ~50% of species on earth
e.g. dinosaurs (other than birds). Several marine invertebrate groups. An astroid hit, the dust from it would block the. sun, this would stop photosynthesis, and food chains.
Adaptive radiations
Rapid speciation and evolutionary change in underexploited habitats. They have a small # of competitors. Many species come to be in a short period of time. They start to differ from each other very quickly.
Two types of Adaptive radiations
Regional: Eg. colonisation of new island chains
World-wide: It can recover diversity after a while.
– Following mass extinction events.
– Only surviving lineages can radiate!
– Replacement in fossil record
Hawaiian ‘Silversword alliance’ example?
Plant group, endemic to Hawaii (very isolated, ‘young’ island group formed by volcanic activity). ~50 species; great variation in size, shape. All descended from one species, in last ~5 million years. the species are genetically similar to each other.
Adaptive radiation of mammals after End-Cretaceous
extinction?
When there was dinosaurs, all mammals were small-medium sized. After the dinosaurs went extinct mammal became the large land animals.
Complex Adaptations
Adaptations that have many parts to it. All parts are need to preform the function well.
How do complex adaptations evolve?
When ‘Darwinian’ evolution proposes:
– evolution through many small steps. They weren’t very different from what was there. (graduison)
– every ‘step’ should improve fitness
However, natural selection doesn’t have foresight and can’t predict that it will happen in the future.
Camera Eye Example?
A giant squid eye. The lens move forwards and back, while the humans change the shape of the lens. Both have the same function. The eye has many parts to it to make it work.
Some mechanisms for evolution of complex adaptations?
1) Intermediates that are actually capable of
functioning
2) Modification of existing structures with
different functions
3) Larger ‘steps’ (than imagined by Darwin).
* e.g. Changes in developmental regulation
* Origin of novel genes, e.g. Gene duplication
Functioning Intermediates
In many cases, simpler forms of complex structures are functional.
– Evidence: Organs of different
complexity in related species
– Step-wise evolution plausible
Functional eyes of different complexity in different living Molluscs. They are well suited to their biology and environments.
Modification of existing structures
Exaptation: Structures adapted for one function are
coincidently useful for another function. Starting from something that’s already complex. How some dinosaurs had simpler wings for insulation, and how some birds have contour feathers that are quite complicated for flight.
The evolution of developmental regulation?
Mutations affecting genes that control development. Small genetic change can result in large, coordinated changes in phenotype.
Development biology
How complex organisms develop overt their lifetimes from very simple organisms (zygote). Genes that control early stages in development can end up small changes in their expression patents or in their animo acid sequences.
Heterochrony
An evolutionary change in the rate of timing of developmental events.
Orthologous genes
The homology is the result of a speciation event and hence occurs between genes found in different species.
Homeotic genes
Master regulatory genes
Hox genes
Control identity of segments along developing animal body.
Fruit fly example?
The wild type fruitfully and homeotic mutant only are different by just a couple of nucleotide difference (in the Hox genes). The mutant grows up to be an adult but wouldn’t do well in nature.
Difference between a nucleotide sequence and changes in regulation of gene expression?
A change in nucleotide sequence may affect its function whenever the gene is expressed, while changes in the regulation of gene expression can be limited to one cell type. Thus a change in the regulator of a developmental gene may have fewer harmful side effects than a change to the sequence of the gene.
Hemoglobin Example?
hemoglobin and myoglobin both carry oxygen. When your muscle needs oxygen it takes it from the myoglobin, which takes it from the hemoglobin. The hemoglobin circulates in blood to get recharged with oxygen. Hemoglobin have 4 polypeptides together, and two subtypes alpha and beta which are different proteins. It is because gene duplication resulted in hemoglobin and myoglobin, then it happened again to get the alpha and beta.
Gene Duplication
How new genes evolve. During DNA synthesis that process mitosis copying of one segment of DNA twice, it can also happen in meiosis called unequal crossing over. Once this happens the genes are at two separate loci, and are independent of one another. Over time they can have evolutionary changes and acquire new differences. These are paralogs.
Paralogs
The two related genes in one genome.
Another way to get new genes?
Lateral/Horizontal Gene Transfer
