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ISCI 350 > Legacies > Flashcards

Legacies Flashcards

1
Q

does natural selection produce “perfect” organisms

A
  • no
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2
Q

what are some reasons that natural selection may produce “imperfect” individuals/limitations of NS (5)

A
  • historical legacies or path dependency
  • lack of variation
  • time lags
  • trade-offs
  • genetic drift
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3
Q

limitations of NS: historical legacies (2)

A
  • natural selection acts to modify existing features; thus, organisms are constrained by their evolutionary history
  • natural selection is a “tinkerer” not an “engineer”
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4
Q

limitations of NS: examples of historical legacies (3)

A
  • panda’s thumb
  • upper respiratory tract of mammals
  • human childbirth
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5
Q

limitations of NS: historical legacies

- panda’s thumb

A
  • panda’s thumb is not a digit, but a modified wrist bone
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6
Q

limitations of NS: historical legacies (2)

- upper respiratory tract of mammals

A
  • we choke easily due to crossing on respiratory and digestive tract
  • due to fish ancestry: lungfish ancestor had lungs used occasionally that crossed with the digestive tract
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7
Q

limitations of NS: historical legacies

- human childbirth (2)

A
  • large brains, bipedality, and egg-laying ancestors of humans push the envelope of evolution
  • human childbirth is very difficult because human babies can barely make it through the birth canal
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8
Q

simplified phylogeny of tetrapods (4)

A
  1. hard-shelled amniotic egg
  2. viviparity: giving birth to live offspring
  3. well-developed placenta
  4. bipedality and large brains
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9
Q

limitations of NS: lack of variation

A
  • natural selection depends on existence of appropriate variants, which arise through mutations, a process RANDOM with respect to the direction of evolution
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10
Q

limitations of NS: examples of lack of variation (2)

A
  • disease emergence

- beetle adaptations to novel host plants

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11
Q

limitations of NS: lack of variation

- disease emergence

A
  • new variants needed for disease emergence (mutations that allow for fitness valleys to occur)
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12
Q

limitations of NS: lack of variation

- beetle host adaptations

A
  • beetle species lack genetic variability to shift to phylogenetically distant host plant species
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13
Q

limitations of NS: time lags (2)

A
  • organisms typically lag behind their environment: the are adapted to conditions in their immediate past, not their future
  • red queen hypothesis: organisms are “running” to keep up with environment through NS, but always stay behind environmental changes
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14
Q

limitations of NS: examples of time lags (4)

A
  • myopia
  • type II diabetes
  • lactose malabsorption
  • allergies and autoimmune disorders
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15
Q

limitations of NS: time lags

- type II diabetes

A
  • it is very common in populations exposed to feast and famine: ‘thrifty genotype’ hypothesis
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16
Q

thrifty genotype

A
  • populations exposed to feast and famine had maximum metabolic efficiency
  • fat deposition at times of plenty and survival at times if famine
17
Q

examples of thrifty gene phenotypes

A
  • replenish skeletal muscle

- store glucose and TG in adipose tissue

18
Q

thrifty genotype stages (3)

A 
PHYSICAL ACTIVITY (hunt or gather)
1. feast: intake of glucose and fat
RELATIVE PHYSICAL INACTIVITY
2. thrifty storage:
- replenish skeletal muscle
- store glucose and TG in adipose tissue
MORE THRIFTY = MORE LIKELY TO SURVIVE FAMINE
3. famine & activity:
- decrease glycogen and TG stores
CONTRACTING SKELETAL MUSCLE
19
Q

what changes are made to the ‘thrifty’ genotype in modern lifestyles (3)

A
  • feast: unlimited food supply with no exercise; skeletal muscle & TG stores NOT decreased
  • thrifty storage: fuel is shunted into greater and unhealthy stores (metabolic syndrome)
  • no famine & activity phase
20
Q

what are the results of the ‘thrifty genotype’ in the modern lifestyle (3)

A
  • obesity
  • type II diabetes
  • cardio vascular disease
21
Q

‘thrifty genotype’ hypothesis (2)

A
  • populations exposed the longest to modern life style (Europeans) may have (partially) weeded out ‘thrifty genes’ as those susceptible in environment died/had lower fitness
  • most of humanity is poorly adapted (at least, metabolically) to our modern lifestyle
22
Q

metabolic syndrome

A
  • type II diabetes
  • obesity
  • cardio vascular diabetes
23
Q

thrift phenotype hypothesis

A
  • metabolic programming due to malnutrition during fetal development may lead to metabolic syndrome when there is excess food later in life
24
Q

drifty genotype hypothesis

A
  • released from heavy predation, genetic drift led to accumulation of mutations that cause diabetes/obesity
25
Q

lactase

A
  • enzyme necessary for digesting of lactose, a protein abundant in milk
26
Q

lactose intolerance (2)

A
  • lactase production switches off during infancy in most mammals and people
  • many of us are unable to digest lactose as adults
27
Q

lactase persistence

A
  • in some human populations, gene controlling lactase production mutated so lactase production is not switched off
28
Q

hypotheses of lactose malabsorption (3)

A
  1. to take advantage of easy supply of milk from herds of pastoral animals
  2. promotion of calcium uptake in high latitude populations prone to vitamin D deficiency
  3. to use milk as alternative source of water, where water is scarce
29
Q

what hypothesis of lactose malabsorption is correct?

A
  • phylogenetic methods show that lactase persistence is associated with pastoralism, not with aridity or solar radiations
30
Q

potential issue of testing lactose malabsorption theories

A
  • ethnic non-independence when comparing between different ethnicities of people
31
Q

limitations of NS: trade-offs

A
  • selection acts on different aspects of the life cycle of individuals: features favoured at one stage may be disfavoured at others
32
Q

limitations of NS: trade-offs

- stages and aspects NS can act on (4)

A
  • adult -> mating pairs: sexual selection
  • mating pairs -> gametes: fecundity
  • gametes -> zygote: gametic selection
  • zygote -> adult: viability
33
Q

limitations of NS: trade-offs

- examples (2)

A
  1. natural selection vs sexual selection

2. longevity vs fertility

34
Q

are all features of organisms adaptive?

A
  • no, some may result from laws of physics or chemistry

- might be shaped by chance (drift)

35
Q

does NS lead to high complexity

A
  • no
36
Q

can the course of evolution be predicted

A
  • no

ISCI 350 (14 decks)

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