Lecture 7: Early Life & Natural Selection Flashcards
Roughly how long ago did life appear
3.5 Ga
What was the isotopic signature that helps us date life?
The presence and concentration of unstable C-14 compared to the stable C-13 and C-12.
What was the fossil evidence that helps us date life?
stromatolites that are 3.5Ga trap sediments
What was the early earth like in terms of atmosphere and light?
The sun was 20% less bright.
There was a reducing atmosphere of methane and ammonia (no O2)
No ozone to shield the earth from UV light
High rates of meteor bombardment
What was the great oxidation event?
When cyanobacteria developed photosynthetic abilities and began producing oxygen as a side product –> was a “catastrophe” to life because many organisms were facultative anaerobes and died
- aka oxidation resolution
What is the evidence of the great oxidation event?
banded iron formations and red beds
What are banded iron formations and how do they form?
Ancient oceans were rich in Fe2+ ions coming from below the crust –> the new dissolved O2 from cyonabacteria combined with the free iron to form iron oxide which sunk to the bottom of oceans, providing red bands of iron oxide.
What are red beds and how do they form?
Exposed red “rocks” that contain iron in them and react with oxygen in the air to form red beds.
What were Darwin’s two main theories?
- Tree of life
- Natural selection
What is the tree of life theory?
All species originate from a other species through evolution (and maybe just one common ancestor)
What is natural selection?
The idea that organisms in a population differ in traits and the individuals with an advantageous trait can survive and reproduce better than individuals lacking that trait, meaning evolution is based on a changing genotype.
What was Lamarck’s theory of inheritance of acquired traits?
Individuals are shaped by their environments. Organs which are needed are used more and become more powerful; those that are needed less are used less and deteriorate.
What is evolution?
A change in allele frequency in a population over time, driven by fitness.
What is fitness?
Reproductive success
Are all differences in traits heritable?
No! some are phenotypes (interactions between genotype and environment) and some are due to plasticity (purely environmentally)
Why do genetics vary between individuals?
random mutations
different modes of reproduction
How do prokaryotes transfer genetic info from generation to generation?
One enzyme breaks apart the two DNA strands. A second enzyme attaches complementary bases to each of the old strands. A third enzyme checks for mistakes (proof- reading) and a fourth DNA repair enzyme fixes them. This results in two strands virtually identical to the original
What is binary fission?
Asexual reproduction in prokaryotes, creates new prokaryotes, and some genetic diversity occurs only via mutation.
What are other ways to transmit genetic information?
Conjugation
Transformation
Transduction
What is conjugation?
Sharing plasmids (separate ring of DNA).
Does not mean reproduction but does introduces genetic variation.
What is transformation?
When a prokaryote picks up a plasmid from the environment.
Does not mean reproduction but does introduces genetic variation.
What is transduction?
A virus relocates DNA from one prokaryote to another.
Does not mean reproduction but does introduces genetic variation.
How does reproduction occur in eukaryotic single cells?
Mitosis: chromosomes are duplicated within a cell and are pulled apart, resulting in two identical daughter cells.
Meieosis: a single set of chromosomes reassort themselves within a cell and then separate, resulting in two daughters each with half a genetic code.
What are the costs of eukaryotic reproduction?
- Two parents needed –> mate searching
- Competition (animals compete for a desirable mate)
- Display costs (animals try to look pretty to find a mate)
- Only half the population generates offspring
What are the benefits of sexual reproduction?
- DNA repairing mechanisms
- masking mutations
- higher genetic diversity
