Cancer Flashcards
cancer
- disease of the DNA where malignant cell lineages grow at the expense of surrounding tissues and, eventually, the entire organism
cancer development (2)
- organisms have multiple controls to prevent or delay cancer
- tumours eventually escape control by a process of evolution by NS at the cellular/tissue level
how are cancer cells selection for
- among cancer cells, NS favours mutant cell lines that are less and less responsive to growth-controlling forces of the organism
cancer conflict
- involved a conflict between the individual (organism) and the cell lineage (cells)
apoptosis (2)
- cell self-sacrifice (programmed suicide)
- involved in:
- sculpting of organism during development
- eliminating old, damaged, or malfunctioning cells
- eliminating infected or malignant cells
cancer vs apoptosis
- cancer (3)
- cell selfishness
- favoured by cell-level selection
- opposed by organismal-level selection
cancer vs apoptosis
- apoptosis (3)
- cell altruism (one sacrifice for well-being of population)
- opposed by cell-level selection
- favoured by organismal-level selection
examples of conflict across levels of organization (4)
- individuals in populations or in social groups
- cells in multicellular organisms
- organelles in cells
- transposable elements in genomes
outcome of conflict between levels
- compromise of selection acting at each of the levels
compromise of selection at different levels
- depends on balance of
1. amount of genetic variance at each level
2. relative rate of turnover of the units at each of the levels
can NS happen at any level?
- yes, as long as units at each level fulfill Darwin’s 4 postulates of evolution by NS (turnover, variability, heritability, differential [non-random] reproductive success)
examples of multilevel selection (3)
- sex ratio evolution in subdivided populations (social spiders)
- pathogen virulence
- cancer and multicellularity
what proportions of males:females are expected in populations (2)
- 1:1 ratio
- fisher’s sex ratio principle
fisher’s sex ratio principle (2)
- greater reproductive success of rare sex should drive sex ratio to 1:1; 1:1 stable equilibrium ratio
- within-group selection and the case for most species
social spider colonies (3)
- isolated population lineages
- 100s-1000s of colonies grow, proliferate, and go extinct with little or no mixing with one another
- only large colonies give rise to daughter colonies
can biased sex ratios in social spiders be maintained by ‘group level’ selection
yes, Darwin’s 4 postulates apply at the colony level in social spiders
social spider colonies: turnover (2)
many colonies with high turnover:
- 100s-1000s of colonies
- high colony turnover
social spider colonies: heritability and variation (2)
heritable variation at the colony level:
- colonies founded by one to a few females
- little or no mixing (gene flow) among colony lineages
social spider colonies: differential (non random) reproductive success
colony-level advantage of overproducing females
- only large colonies give rise to daughter colonies
why do young social spider colonies have more femae-bias
- younger colonies have had less time for within-selection to act
how does migration rate affect female-bias in social spider (2)
- more migration = less variation between-colonies
- more migration will favour 1:1 sex ratio/within-colony selection
sex-ratio: when only large cells proliferate (2)
- no matter the starting ratio, the ratio will tend toward a heavily female-biased ratio
- favour between-colony selection
sex-ratio: all colonies are equally likely to proliferate (2)
- no matter the starting ratio, the ratio will tend toward 1:1
- favour within-colony selection
sex ratio: within-group selection only
- 1:1 sex ratio
sex-ratio: between-group selection only
- heavily female-biased sex ratio
sex-ratio: within and between-group selection
- balance/compromise between selective forced would lead to a equilibrium ratio between 1:1 and 1:10
social spider selective forces
- within colonies (2)
- fisher’s principle: greater reproductive success of rare sex
- 1:1 sex ratios
social spider selective forces
- between-colonies (2)
- greater productivity of colonies
- female-biased sex ratios
what factors determine equilibrium values (3)
- migration rate
- propagule size
- group turnover rate
more female-biased sex ratios evolve at: (3)
- lower migration rates
- smaller propagule size
- greater group turnover
propagule size
- size of founding groups
how does lower migration effect variance and proportion males (3)
- lower within-group variance
- higher between-group variance
- lower proportion males
how does high turnover rate effect selection and proportion males (3)
- strong between-group selection
- weaker within-group selection
- lower proportion males
how does low propagule size effect variance and proportion males (3)
- lower within-group variance
- higher between-group variance
- lower proportion males
equilibrium sex ratios
- reflect a compromise between group and individual selection
when does group level selection have the upper-hand (3)
- smaller within-group variance
- larger between-group variance
- larger rates of turnover
pathogen virulence: when does within-host selection predominate
- high transmission and low population subdivision
- greater virulence
pathogen virulence: when does between-host selection predominate
- low transmission and high population subdivision
- lower virulence
pathogen virulence: within-host selective forces
- faster growing strains win due to higher virulence
pathogen virulence: between-host selective forces
- strains that maintain hosts alive longer win
- less virulence
what is the trade-off between transmission and virulence
- greater virulence is expected when there is greater opportunity for horizontal pathogen/parasite transmission
virulence with horizontal transmission
- more transmission -> higher pathogen virulence
virulence with vertical transmission
- less transmission -> lower pathogen virulence
cancer: within-individual selective forces (2)
- greater cell lineage proliferation
- cancer
cancer: between-individual selective forces
- greater survival of individual
- apoptosis, cancer control
how does age affect cancer (2)
- organisms with later age have more cancer as rate of turnover is very slow compared to cell turnover rate
- selection to prevent cancer is not strong in late life
cellular slime molds
- form multicellular structures by aggregation
cancer variance
- variance description
- mechanisms (2)
reduces variance within while maximizing variance among organisms:
- origin from single cell
- DNA repair, apoptosis, cell senescence
cancer turnover
- turnover description
- mechanisms (2)
minimize within-organism turnover
- germ-line sequestration
- secondary somatic differentiation
- localized cell subpopulations
germ-line sequestration (2)
- cells that give rise to gametes are set aside during early development so no mutations accumulate from additional proliferation
- somatic cells, which arise from the zygote during mitosis, cannot get into the germ line and are genealogical dead ends
germ-line sequestration and turnover (2)
- makes germ cell turnover more equal to human turnover, especially in females
- reduces strength of within-organism selection
secondary somatic differentiation
- ancestral mode
- cell lineage must remain mitotically active to replenish somatic lineages incapable of re-differentiation
secondary somatic differentiation
- humans
- cell lineage is released from duty of producing somatic tissues because multipotent stem cells give rise to somatic cells in different states of differentiation
secondary somatic differentiation
- drosophilia (2)
- only 13 divisions separate zygote from cells that will become gametes
- minimizes chances of mutation
secondary somatic differentiation
- humans
- germ cells are set aside in 56-day embryo to remain sequestered for over 1-3 decades/until puberty
compartmentalized cell subpopulations (2)
- somatic cells are asexual, so cancer can only develop if multiple oncogenic mutations accumulate in the same lineage
- it takes longer for this to happen when local populations are small or don’t persist for long; also prevents variance within the cell population
compartmentalized cell subpopulations
- example
- subpopulation structure in intestinal tissue architecture
although organism has the upper hand, why is cancer still a possibility (2)
- many generations of cell turnover involving millions of mutating cells occur in the soma
- success of cancer control mechanisms declines as strength of organismal-level selection declines with age
how do organisms generally delay cancer onset
- gargantuan mechanism of control by the organism
cancer: organism mechanisms of control (5)
- DNA repair
- cell-cell communication
- oncogene suppression
- tumour suppression by p53 and others
- apoptosis and cell senescence
T or F: senescence has evolved to eliminate the old and make room in population for the young (2)
- false
- unlikely that population selection is working here as Darwin’s four postulates need to be met
- within-population selection would likely override between-population selection
T or F: menopause evolved to protect human gene pool from spread of genetic defects (2)
- false
- unlikely that species selection is working here as Darwin’s four postulates need to be met
- within-species selection would likely override between-species selection
