Introduction to Evolution 2 Flashcards
What is the RNA world hypothesis based on?
It is based on the ability of some RNA molecules to have enzymatic activity. It is thought that early lide is thought to have been based on self-replicating, self-catalyzing RNA molecules.
What is the RNA world hypothesis?
It is based on life later evolving to use DNA and proteins due to RNA’s relative instability and poorer catalytic properties.
The RNA world evolved into a DNA genome/protein enzyme worlds with the intermediate being proteins. DNA is more stable than RNA and so has greater range and robustness of protein enzymes.
How has the cell evolved?
- The earliest cells are prokaryotic - pro (before), karyon (nucleus)
- It is thought that over time the DNA and protein became surrounded by phospholipids (beginning of a membrane) and that in the fossil records leads rise to the emergence of bacterial/archaeal cells (that look similar).
- All bacteria, archaea and eukaryotes carry genetic material in DNA.
- Eukaryotes and archaea use the same amino acid in the beginning of each protein and that’s methionine, whereas bacteria use a modified version of methionine called formyl-methionine.
LOOK AT NOTES TO SEE THE FEATURES OF THE THREE DOMAINS.
LOOK AT NOTES TO SEE THE FEATURES OF THE THREE DOMAINS.
What is the theory behind how the eukaryotic cell has risen?
There is evidence that the eukaryotic cell has risen by a process called endosymbiosis (generated other organelles and the nucleus).
A modern eukaryotic cell contains chloroplast and mitochondria which are collectively knowns as plastids.
The mitochondria shares similarities with an aerobic bacterium while chloroplasts share similarities with the cyanobacterium.
Eukaryotic cells contain a nucleus, organelles and plastids (mitochondria/chloroplasts).
Eukaryotic cells arose through endosymbiosis or predation α-protobacteria (ancestral) and archeal host engulfing bacteria which survives and persists.
LOOK AT DIAGRAM TO SEE PROCESS
What is the evidence for endosymbiotic evolution?
- Mitochondria have their own circular (not linear DNA) genome which replicates independently of nuclear DNA.
- New mitochondria are produced by fission of existing mitochondria, much like bacteria dividing.
- If you sequence mitochondrial DNA you will observe that the mitochondrial genome all share similarities with the Typhus bacterium called Rickettsia prowazekii.
- All mitochondrial genomes share similarity with the Typhus bacterium Rickettsia prowazekii.
- Rickettsias are obligate (have to), intracellular parasites or symbionts of eukaryotes, in other words this means that Rickettsiales have to live inside a eukaryotic cell to survive.
- For Evidence for endosymbiotic evolution of eukaryotic cells, a phylogenetic tree can be used to look at the molecular relationships between DNA. More specifically, a Phylogenetic tree based on plastid vs bacterial DNA.
- Where it’s evident that Chloroplast genomes all resemble cyanobacterial DNA
What is special in the plastid genomes?
- Plastid genomes encode proteins necessary for plasti function.
- It is observed that there is a loss of genes compared to ancesterol form. Those genes have either been transferred into the nucleus (into the nuclear DNA of the eukaryotic cell) or their functions have been taken over by things that are present in the nuclear DNA, so ‘lost’ genes are present in the nuclear genome.
- Multicellularity is a (geologically) recent trait of eukaryotes (1 and half billion years ago).
- In order of appearance in fossil record: eukaryotes -> multicellular life -> animals.
- Complex, multicellular organisms are even more recent but the (apparent) rate of diversification increases with multicellularity.
How did multicellularity and complex organisms evolve?
-Multicellularity is usually a characteristic of eukaryotes
-There are 4 basic processes of multicellularity:
1. Spatial organization: get into the right place
2. Change in form: cells need to specialized, for
example the neurons can perform very specialized
functions but on its own it’s not going to survive
very long.
3. Growth: how cells grow together in a coordinated
way (doesn’t happen in cancer)
4. Differentiation: cells have to be able to control their
differentiation
What is an example of the evolution of multicellular organisms?
-So first question is: What does it take to make an eye?
At the very basic level you need a photoreceptor (detects light).
-To make it better – you can have a lens (focuses light on photoreceptor making it more sensitive).
-To make it really fancy – put all this into a dark box so now it’s just picking up light from one side (one direction) this can be controlled through a hole or aperture (control amount of light going into the eye).
-Morphological (shape) comparison suggests that eyes have evolved over 40 times.
What are homologues, paralogues and orthologues?
-Homologues are related by descent from a common ancestor. There are 2 forms:
-Paralogues are homologues within the same species
(duplication within a species) - e.g. Mouse Hox a1, a2,
a3, a4 etc are paralogues.
-Orthologues are homologues between species - eg
the fruit fly Antennapedia gene in the fly is the
orthologue of mouse Hox a6, b6, c6.
How do mammalian limbs develop?
- At one point the bat embryo looks similar to a human embryo (the limb bud) over the next couple of weeks the bat embryo will somewhat change. Where there will be extended radius, ulnar and digits.
- Prx1 gene is important in the rate at which cells divide.
- Increase in digit length in the bat is partly controlled by extending the duration of Prx1 expression in the embryo by changes in its regulatory domain (promotor).
- This could be experimented in a mouse embryo.
Where did Homospaiens come from and what do we known?
- There is evidence from the fossil record and also from molecular analyses.
- Mitochondria are maternally (from mother) inherited, because mitochondria are excluded from the sperm before fusion with egg.
- The mitochondrial genome replicates independently of the nuclear genome and does not undergo recombination (mixing).
- Similarly, the male Y chromosome does not have a homologous female chromosome to recombine with.
- Therefore, the changes in sequence of mtDNA and the Y chromosome are due to random mutations over time and not by gene shuffling (recombination).
- Analysis of mtDNA and Y chromosome sequence shows maternal and paternal origin, respectively.
What can we look at to find the common ancestor of humans?
- If you look at mitochondrial DNA sequence you will find that long ago there was a common ancestral form in east Africa. As the group migrate and become isolated the changes that occur are random (by chance) and due to mutations. We can trace the route of migration across the globe by looking at changes in mtDNA sequence.
- The same can be done for Y chromosome sequences by tracing human migration.
How has genetic variaiton amongst homosapiens occurred?
- Most modern humans are related to a group of people that migrated out of Africa about 65,000 years ago.
- Homo sapiens made friends during their migration from Africa, the Neanderthals and denisovans.
- You can find traces of Neanderthal DNA in modern Europeans and Denisovan DNA towards Asia.
