evolution Flashcards
How is gene duplication a key driver in evolution?
When a gene is duplicated, the original gene can go back to executing it’s original function. The duplicated gene, however, is free to be modified.
It may perform functions complementary to the original gene’s function (acting as a backup). It may also, over time, evolve non-overlapping functions.
What is molecular homology?
Molecular homology is determined from amino acid or nucleic acid sequence.
- two genes from the same organism (by duplication) are called PARALOGS
- two genes from different organisms (common ancestor) are called ORTHOLOGS
What is molecular analogy?
It’s also known as molecular convergence.
It’s when proteins have the same function with no structural identity.
An example would be crystallins (lens proteins)
There are many different transparent proteins in different species. They all have other functions (in addition to being stable, transparent and refractive).
What do we mean by the term homologous?
We say two structures are homologous when they are derived from a common ancestral version.
Because these structures are derived from a common ancestor, they form by a common mechanism.
An example would be tetrapod limbs.
What is the Cambrian Explosion?
It is the rapid appearance (and disappearance) of complex organisms in the fossil record (about 525 million years ago).
What are some requirements for radiometric dating?
- the rate of radioactive decay is constant: not affected by temperature, pressure, chemicals, electrical or magnetic fields
- the parent and daughter nuclides cannot leave or enter material after it is formed
- there must be no intrusion of other, later rock
- there must be no contamination
What is radiometric dating?
It is measuring the ratio of parent/daughter nuclides.
Radioisotopes can be used to date rocks and fossils.
How does a bacteria culture evolve the ability to utilise citrate?
The ability of bacteria to utilise citrate is controlled by its citrate gene, which is controlled by the citrate promoter. The gene is normally turned off in the presence of oxygen. It happens to be situated next to the RNK promoter, which controls the RNK gene. This is turned on in the presence of oxygen.
It was found that, in cultures that were able to utilise citrate, the citrate gene and RNK promoter were duplicated right after each other. This didn’t affect the existing citrate gene, but the duplicated citrate now has an RNK promoter before it. This meant that the citrate gene would now work in the presence of oxygen.
How can we observe evolution?
1) Obtain 12 colonies of E. Coli from a single clone
2) Subculture it every day, for 27 years
3) Freeze the culture samples every 500 generations (75 days)
4) Over the completed experiment, 63,500 generations would have been observed
5) We then test the cultures for the ability to grow in citrate in the presence of oxygen
The ability to use citrate evolved after about 30,000 generations in one group in particular. Earlier generations from this same ancestral E. Coli were repeatedly able to evolve the ability to utilise citrate at about the same time.
Describe the rapid evolution of influenza virus by reassortment.
Different flu strains infecting the same cell can swap parts of their genetic material.
This is why the 2009 (and 2010) H1N1 strain contains alleles from human, avian and swine flu.
