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BIOL 336 > Adaptations & Traits 1 > Flashcards

Adaptations & Traits 1 Flashcards

1
Q

what “pushes” evolution

A
  • selection and drift
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2
Q

what “persists” the push of evolution

A
  • genetics + development
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3
Q

genetics (2)

A

small scale: population genetics

big scale: phylogeny

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4
Q

an adaptation

A
  • A TRAIT or an integrated set of traits that has evolved by natural selection
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5
Q

adaptation

A
  • A PROCESS in which the traits of a population change over generations (evolve), resulting in individuals that are better able to survive/reproduce
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6
Q

an adaptation for X

A
  • a trait or an integrated set of traits that has evolved by natural selection involved X as a selective pressure
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7
Q

why should we be cautious when interpreting traits as adaptations (2)

A
  • trait might be an adaptation, but not for the function stated
  • trait might not be an adaptation at all
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8
Q

evidence for adaptive origin (2)

A
  • among species, purported selective force is associated with the trait repeatedly
  • phylogeny shows replicate origins of the trait, in each case in the context of the selecting condition
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9
Q

when are adaptations “for X” (2)

A
  • when selection for X was involved when the trait was originally established in an ancestor long ago
  • when the trait is currently being maintained by selection for X
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10
Q

how could we demonstrate a trait is currently being maintained or established by natural selection (4)

A
  1. variation: there is variation in traits in the population
  2. genetics: the variation is heritable
  3. fitness: trait affect function related to the proposed selective mechanism
  4. fitness: there are measurable effects of the trait on survival and reproduction
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11
Q

ancestral constraints

A
  • traits inherited from an ancestor that are difficult to change, and which are suboptimal or limit subsequent adaptation
  • eg: the crossing of our airway with the passage of food, small pelvic girdle that makes giving birth difficult
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12
Q

ancestral baggage: food and air pathways (3)

A
  • our food and air pathways cross, leading to risk of choking
  • our fish ancestors evolved lungs to supplement gills in the belly and below the gut, but the air is above at the water surface: the two paths crossed, but it was okay because air was only breathed occasionally
  • now we require air constantly so its a bad idea that the paths cross; but, our whole developmental system is committed to this arrangement and there would be MANY mutations that would be needed to change it and genetic variation is not available for this
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13
Q

ancestral baggage: pelvic girdle (3)

A
  • evolved to provide support for limbs by connecting them to spine and to each other in fish ancestor; thus, it surrounds our reproductive system and babies must pass through pelvic on way out
  • no problem for eggs to fit through pelvic girdle in fish very challenging for humans who have babies with large brains and smaller pelvises to walk upright
  • many mutations are needed to re-route reproductive system through the tummy; it is difficult to undo 450 millions years of commitment
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14
Q

what are the consequences of the reproductive system going through the pelvis (5)

A
  • human babies must be born before fully developed, so they are dependent on their parents for many years
  • mother’s pubic bones must temporarily separate
  • baby’s skull must remain flexible
  • during birth process, baby has to twist sideways (for head), then backwards (for shoulders)
  • mother needs assistance for birth
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15
Q

maladaptive intermediates

A
  • fitness valleys where the phenotype is not desirable for survival/reproduction, but must be overcome to achieve a different fitness
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16
Q

by what mechanism could adaptive valleys be crossed

A
  • in small populations, selection is less effective, and genetic drift (chance effects) could cross valleys
  • selection varying through time might raise the valley momentarily
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17
Q

lack of foresight or vision of possibilities (2)

A
  • natural selection can see only the small amount of variation currently in the population, it cannot see distant possible phenotypes
  • there are no direct paths to better phenotypes, so we may be sitting at any place in a fitness landscape
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18
Q

natural selection operates without any foresight (2)

A
  • natural selection choose among alternatives that already exist
  • these alternatives are generated randomly (through mutation, recombination, meiosis and sex)
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19
Q

why can cause an organism to be less than perfect in any given trait (4)

A
  • ancestral constraint
  • population genetic complications
  • inconsistent selection
  • trade-offs
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20
Q

what are some population genetic complications (6)

A
  • drift
  • dominance
  • mutation pressure
  • linkage/meiosis
  • lack of genetic variation
  • epistasis
21
Q

trade-offs

A
  • perfection in one trait conflicts with perfection in another
22
Q

inconsistent selection

A
  • selection can vary over space or time
23
Q

epistasis

A
  • alleles have no good effect until combined
24
Q

lack of genetic variation

A
  • good mutations aren’t available
25
Q

linkage/meiosis (2)

A
  • good alleles are linked to bad alleles

- good combinations of alleles are broken apart by meiosis

26
Q

mutation pressure

A
  • deleterious mutations keep happening
27
Q

dominance (2)

A
  • a beneficial recessive allele is not seen initially by selection because it is hidden in heterozygosity
  • difficult to get rid of the last few copies of a deleterious recessive allele
28
Q

drift (2)

A
  • beneficial allele might be lost by bad luck when at low frequency
  • mildly deleterious allele might drift to fixation
29
Q

senescence (2)

A
  • deterioration with age due to “faults” in our development

- NOT just inevitable wearing out with metabolism

30
Q

how do we know that selection could have improved longevity, but didn’t (2)

A
  1. longevity can be selected for

2. organisms with different amounts of cell are equally resistant to cancer

31
Q

what are the two types of challenges an organism faces (2)

A
  • extrinsic damage: bad luck

- intrinsic damage: your genes fault

32
Q

extrinsic damage (3)

A
  • death/injury/illness from causes for which your genes can’t help much
  • accidents, predation, diseases, weather, etc
  • selection cannot help with this; however, causes early selection to be much stronger than later selection as old-age individuals are so likely to die anyways -> makes early-goof effect have more power than late-bad effect
33
Q

intrinsic damage (3)

A
  • death/injury/illness from developmental or survival issues that genes could have solved
  • cancer or heart attacks
  • selection could solve this, but did not
34
Q

senescence theory

A
  • if extrinsic damage tended to kill our ancestors when they were old, then intrinsic damage would have evolved to kill us when we are old also, even if we are protected from extrinsic damage
35
Q

what are the two main theories of senescence (2)

A
  • mutation accumulation theory: random effects

- antagonistic pleiotropy theory: trade-offs

36
Q

mutation accumulation theory (3)

A
  • late-acting deleterious mutations accumulate because they are weakly selected against
  • individuals rarely live that long due to extrinsic damage, and therefore there is almost no loss of reproduction in late-acting mutations
  • ultimately reduces intrinsic longevity due to the failure of selection to act and random effects (mutation and drift)
37
Q

how can cancer involve somatic mutations AND run in families

A
  • the susceptibility to somatic mutations if inherited; the somatic mutations themselves are not inherited
38
Q

according to the MA theory, what happens to organisms if they are protected against extrinsic damage

A
  • they still senesce and die due to the accumulation of late-acting damaging mutations
39
Q

antagonistic pleiotropy theory

A
  • deleterious mutations that act in old age were selected for because of their beneficial effects in earlier life
40
Q

pleiotropy

A
  • a gene has more than one effect
41
Q

antagonistic

A
  • the different effects oppose each other; in our theory, the early effect is good and the late effect is bad
42
Q

what is an example of an antagonistic pleiotropy mutation

A
  • a mutation that acts early to increase fertility, but then acts later to decrease health and longevity
43
Q

is it reasonable to suppose there would be such pleiotropic genes that increase early fertility at the expense of late health? (2)

A
  • yes: there are limited resources and thus tradeoffs

- spending our resources early may damage late health

44
Q

would antagonistic pleiotropic genes be selected for? (2)

A

potentially, because:

  • high rates of extrinsic damage
  • the advantage of early reproduction (could cause these genes to be selected for instead of just passively accumulating)
45
Q

what is the advantage of early reproduction (3)

A
  • even if there were no extrinsic damage, it is better to reproduce early than late because early reproducing genes get a shorter generation time and therefore, multiply faster
  • gaining early babies more than compensates for losing late ones
  • essentially, a genotype that starts reproduction earlier will outcompete a slower one because it will multiple faster if all else if equal
46
Q

what is the challenge of increasing human longevity

A
  • humans likely have thousands of late-acting damaging genes, some accumulated because selection against them was weak and others selected for due to their early-good effects
47
Q

how do we know that lifespan is NOT a simple function of heartbeats, metabolism, and a body “wearing out”

A
  • bats and rats both have small size and high metabolism; however, bats live much longer than rats
48
Q

why are bats able to live so long

A
  • they have low extrinsic damage rates, so selection was effective at weeding out deleterious late-acting alleles
  • they have low extrinsic damage rates due to low predation: they forage at night and roost in caves

BIOL 336 (13 decks)

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