Major Transitions Flashcards
Three Domain Hypothesis
The three domains consist of archaea, bacteria, and eukaryota
-Eukaryota is the sister domain of archaea
Eocyte Hypothesis
Proposes that archaea is paraphyletic and Eukaryota is a subclade of archaea
-If hypothesis is correct, the only domains would be archaea and bacteria
Staying Together
Multicellularity arose when cells from a unicellular ancestor remained together after cell replication
-more common and explains most multicellular cases in plants and animals
-“Unicellular Bottleneck”: A single cell divides but does not separate and continues to grow
Coming Together
Involves free-living cells that joined together during evolution of multicellularity
-Produce a unicellular unit
-May or may not be genetically similar; dissimilar genetics leads to genetic conflict (causes cells’ reproductive interests to differ, hence why selection leans towards staying together
Somatic Cells
Cells in the body that grow and maintain a multicellular organism
-Any cells that is not sperm or eggs
Germ Cells
Cells of a multicellular organisms that are specialized for reproduction (eggs and sperm)
Individual
Indivisible wholes that can reproduce and pass on heritable variations to their offspring
-natural selection can act on these variations and gradually produce incremental improvements on these heritable traits
Social Group
Set of individuals who affect each others fitness
What are the major evolutionary transitions?
- Origin of eukaryotic cells
- Sexual reproduction
- Evolution of multicellularity
- Complex multicellular life
- Individuality
- Complex social living groups
- Eusocial Groups
What are the characteristics of eukaryotic cells?
- Nucleus
- Membrane bound organelles
-eukaryotic cells are specialized for specific functions
Describe the evolution of chloroplasts, mitochondria, and nucleus in eukaryotes
NUCLEUS:
-Endosymbiosis; organelle and gene migration to the nucleus
-Evidence; neoSTLS2 gene in chloroplast; genome is only resistant to kanamycin if it is in the nucleus…had to migrate to nucleus for protection
MITOCHONDRIA:
-Endosymbiosis of a protozoa by a lager host cell
-Endosymbionts provide their host with energy or food and in return they were protected from danger by residing inside another organism
-Some evidence includes; 1) Mitochondria contains its own DNA 2) Multiple membranes 3) Mitochondria replication similar to bacteria
CHLOROPLAST:
-Chloroplast once formed a symbiotic relationship with cells from another species, providing the cells with chemical energy through photosynthesis, eventually evolving into organelles of the host cell
-were once free-living photosynthetic cyanobacteria
-have their own singular, circular chromosomes similar to bacteria (RNA is more closely related to cyanobacteria than eukaryotes)
Evolution of sexual reproduction (yeast cells, cheater mutation)
Germ cells produce gametes through meiosis and somatic cells produce other cells in the body through mitosis
YEAST:
-Asexual reproduction through staying together route in multicellularity
-Snowflake clusters are clusters of independent yeast cells
-Snowflake clusters are a heritable trait
CHEATER MUTATION:
-Natural selection started favoring strategy in which only a select number of cells would retain reproductive qualities and later become germ cells, causing overrepresentation
-Those who lost the reproductive quality would go on to become somatic cells
-Genomic Imprinting; alleles differentially expressed based on inheritance from mother or father (acts as a factor in preventing cheating and producing pathogenetic copies)
Role of rls 1 and reg A in reproduction
rls 1 in Chlamydomonas (Individuality):
-Gene that is expressed as a function of environmental cues (such as resource depletion), and its expression inhibits the process of reproduction (regulates the timing of cell division in unicellular organisms)
-Was co-opted to become the reg A gene to regulate the differentiation of cells into germ and somatic cells in multicellular volvox species
reg A in Volvox (Individuality):
-Gene expression of reg A causes the suppression of a number of nuclear genes that code for chloroplast protein (cell growth is dependent on chloroplast proteins)
-reg A expressed= cell remains small and produce flagella (form somatic cell)
-reg A not expressed= photosynthesize, grow in size, and can’t produce flagella (form germ line)
Describe the costs and benefits of group living
Benefits:
-Group Foraging (“flushing effect” in fish against predators; forager bees dance for certain amount of time to describe how far food source is)
-Protection from Predators; 1) “Many Eyes Hypothesis” 2) Hydrodynamic Effect 3) Confusing the Predator
Costs:
-Increased Parasite Transmission
Explain “Flushing Effect” in fish as a benefit of social groups
Individual fish help each other out by “flushing out” predators (so others can eat)
-Fish forage as if they were alone
-Prey are harder to catch in vegetation, but easier in open water
