L6 - Early Life Flashcards
1
Q
What are the characteristics of life?
A
- Maintain internal homeostasis
- Respond to external stimuli
- Consume and produce energy
- Reproduce and have a form of heredity
2
Q
What is biological evolution?
A
Gradual change in the inherited traits of a population
3
Q
What two ideas were established during the Darwinian Revolution (1859)?
A
- The Tree of Life: All species on Earth have evolved from other species (perhaps, ultimately, from just one)
- Natural Selection: organisms are well-adapted to their environments because they accumulate, over the generations, traits that enable them to survive and/or reproduce better than organisms lacking those traits
4
Q
What is Larmarck’s theory?
A
- 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 (over successive generations)
- DISPROVED: many real examples and observations that changes that occur in an animal during life are not passed on to the animal’s offspring
5
Q
Key characteristics of Natural Selection?
A
- Individuals in a population differ in their traits
- Some traits confer an advantage depending on the environment
- Individuals that have these advantageous traits survive and reproduce better than others
- Phenotype = expression of trait
- If differences are heritable, the frequency of advantageous traits will increase in the next generation (evolution is due to changing genotype)
6
Q
Define Gene
A
A self replicating DNA unit that occupies a specific location on a chromosome and determines a particular characteristic in an organism
7
Q
Define Allele
A
- A variant form of a given gene (section of DNA) that codes for something, like a trait
- Some alleles are more advantageous than others in certain environments
8
Q
Thus, biological evolution implies…
A
- Change in allele frequencies in a population over time
- Variation in reproductive success = fitness
9
Q
What is fitness?
A
- Reproductive success: how many surviving offspring do you have compared to others in the population?
10
Q
Are all differences in traits heritable?
A
- Phenotype: expression of a trait
- Interaction between genotype and environment
- Plasticity: environmentally determined, non-heritable, trait differences
- i.e., body size, plants growing in high altitudes vs low altitudes, melanin (skin), 3 spine sticklebacks
11
Q
Why do individuals’ genetics vary?
A
- Mutation
- Mode of reproduction (relates to genetic variation)
12
Q
How do prokaryotes transfer information from generation to generation?
A
- Enzyme gently breaks apart the two DNA strands
- Other Enzymes attach complementary bases to each of the old strands
- Another enzyme proofreads and a DNA repair enzyme corrects the mistakes
- Result: two strands virtually identical to the original
13
Q
How does mutation occur?
A
- Random: Occurs because errors/mistakes happen
14
Q
How do prokaryotes reproduce?
A
- Binary fission (asexual reproduction)
- Replication of the circular chromosome followed by the fissioning of the cell
- Transmission of DNA-coded information across generations
15
Q
What are other ways of transmitting genetic information?
A
Conjugation
Transformation
Transduction
16
Q
What is conjugation?
A
- Another form of transmitting genetic information
- sharing plasmids (separate ring of DNA)
- does not = reproduction but introduces genetic variation
17
Q
What is transformation?
A
- A prokaryote picks up plasmid from the environment
- Does not = reproduction but introduces genetic variation
18
Q
What is transduction?
A
- A virus relocates DNA from one prokaryote to another via viral replication cycles
- Does not = reproduction but introduces genetic variation
19
Q
Genetic structure of Eukaryotes?
A
- Hugely different from Prokaryotes
- Much much larger
- Genetic material organized into multiple linear chromosomes (not circular like prokaryotes)
- Each chromosome consists of one long molecule of DNA
- After DNA replication, 2 identical “sister chromatids” form.
20
Q
How do single-celled Eukaryotes asexually reproduce?
A
- Duplication (of chromosomes in Haploid cell)
- Mitosis: duplicate chromosomes line up and are pulled to opposite sides of parent cell
- Fission: cell divides to produce identical daughter cells
21
Q
Eukaryotic sexual reproduction !
A
- Sexual reproduction = Meiosis
- 2 parents with homologous chromosomes (just different evolutionary histories)
- Gametes fuse to form diploid zygote
- Allows for a vast amount of variation on which natural selection thrives
- Once a cell divides: it will have a random combination of chromosomes from the mother cell and the father cell
22
Q
How does meiosis work?
A
- Each homologous chromosome lines up in the centre of the cell randomly
- Once the cell divides, it will have a random combination of each parent’s genetic code
23
Q
Accidents that may occur during meiosis?
A
- Reassortment: homologous chromosomes separate and move to opposite sides of cell
- 2 groups of 3 chromosomes
- More chromosomes there are, more possible combinations in gametes (Humans = 2^23 possible gametes)
- Reassortment and recombination?
- Both are additional sources of genetic variation: more chromosomes, more possible combinations in gametes
24
Q
What are the products of asexual and sexual reproduction?
A
- Identical copies of parents
- Cells remain identical unless a mutation occurs
25
What are the products of sexual reproduction?
- Much greater variation is possible because of reassortment and the mixing of genetic materials from two individuals with different evolutionary histories
26
Costs during eukaryotic sex?
- Mate searching: as populations decrease, it becomes increasingly difficult to find a mate, thus contributing to a population's potential extinction
- Competition (not only for food or space, but now for mates)
- Fundamental costs...
- Only half the population generates offspring
- Every time you reproduce, you break apart well adapted chromosome adaptations while at the same time increasing genetic variation (tradeoff)
- Few eukaryotic species are unisexual (e.g., parthenogenesis-reproduction without fertilization)
27
What conditions favour sexual reproduction? What is the relative probability of surviving in this environment given my genetics and in relation to other individuals in this environment??
- Genetic systems:
- Mutations
- Chromosomes
- Genes/Alleles
- Population Processes:
- Death rate
- Reproduction/birth rate
- Mate searching
- Competition
- Biotic-biotic interactions
- Natural selection:
- Hard selection: extra mortality for maladapted individuals
- Soft selection: no extra mortality, but who dies depends on fitness
- Space & time:
- Movement
- Abiotic-biotic interactions
- Spatio-temporal variability
- Environmental complexity
- Local adaptation
28
Model results...
- Asexual reproducers can reproduce more successfully within a shorter period of time
- However, over long periods of time, sexual producers are better at surviving
29
"Direct" advantages of sexual reproduction
- DNA repair mechanism: the ability to correct mistakes if they are to occur
- Masking mutation: higher chance that one copy will work
30
How did Eukaryotes arise?
- Historical context:
- Diversified prokaryotic life during their emergence
- Oxygenation of the world -- leading to increased efficiency in cell activity (??)
- High complexity: many "organelles"
- Different reproductive approach
- Symbiosis: long-term biological interaction
31
What is the chimeric eukaryote: symbiosis (biotic-biotic interaction)?
- Most of eukaryote cell = Archaea
- Mitochondria = one lineage of Bacteria
- Chloroplasts = another lineage of Bacteria
- Hypotheses on eukaryote origins involve some symbiosis/fusion of prokaryotes that results in the larger, more complex eukaryotic cell
32
What is the biochemical evidence for Eukaryote ancestors?
- Archaean ancestor: DNA sequence data from genes in the nucleus of eukaryotes suggests that eukaryotes are more closely related to Archaea than to bacteria
- Bacterial ancestor: mitochondria and chloroplasts (eukaryote organelles) have their own circular DNA and prokaryotic-type ribosomes, most similar to bacteria.
33
How??
Endocytosis:
- Substance gains entry into a eukaryotic cell
- Cell membrane wraps itself around the particle and pinches off a vesicle inside the cell
