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ENVR 202 > L6 - Early Life > Flashcards

L6 - Early Life Flashcards

1
Q

What are the characteristics of life?

A
  1. Maintain internal homeostasis
  2. Respond to external stimuli
  3. Consume and produce energy
  4. Reproduce and have a form of heredity
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2
Q

What is biological evolution?

A

Gradual change in the inherited traits of a population

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3
Q

What two ideas were established during the Darwinian Revolution (1859)?

A
  1. The Tree of Life: All species on Earth have evolved from other species (perhaps, ultimately, from just one)
  2. 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
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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
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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)
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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

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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
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8
Q

Thus, biological evolution implies…

A
  • Change in allele frequencies in a population over time
  • Variation in reproductive success = fitness
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9
Q

What is fitness?

A
  • Reproductive success: how many surviving offspring do you have compared to others in the population?
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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
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11
Q

Why do individuals’ genetics vary?

A
  • Mutation
  • Mode of reproduction (relates to genetic variation)
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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
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13
Q

How does mutation occur?

A
  • Random: Occurs because errors/mistakes happen
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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
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15
Q

What are other ways of transmitting genetic information?

A

Conjugation
Transformation
Transduction

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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
  1. Duplication (of chromosomes in Haploid cell)
  2. Mitosis: duplicate chromosomes line up and are pulled to opposite sides of parent cell
  3. 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
Q

What are the products of sexual reproduction?

A
  • Much greater variation is possible because of reassortment and the mixing of genetic materials from two individuals with different evolutionary histories
26
Q

Costs during eukaryotic sex?

A
  • 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
Q

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??

A
  • 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
Q

Model results…

A
  • 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
Q

“Direct” advantages of sexual reproduction

A
  • DNA repair mechanism: the ability to correct mistakes if they are to occur
  • Masking mutation: higher chance that one copy will work
30
Q

How did Eukaryotes arise?

A
  • 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
Q

What is the chimeric eukaryote: symbiosis (biotic-biotic interaction)?

A
  • 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
Q

What is the biochemical evidence for Eukaryote ancestors?

A
  • 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
Q

How??

A

Endocytosis:
- Substance gains entry into a eukaryotic cell
- Cell membrane wraps itself around the particle and pinches off a vesicle inside the cell

ENVR 202 (22 decks)

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