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Evolutionary Biology > 7-9 > Flashcards

7-9 Flashcards

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1
Q

5 assumptions of hardy weinburg model

A

a. infinitely large population size
b. no mutation
c. no selection
d. no gene flow
e. random mating

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2
Q

What is fitness

A

the average lifetime contribution of individuals of a given genotype to the population after one or more generations (reproductive success)

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3
Q

What is natural selection

A

A process where indviduals with with favorable traits (phenotypes) are more likely to survive and reproduce than those with unfavourable traits. If the trait is heritable the genotypes/alleles associated with it will increase in frequency over generations

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4
Q

What is an adaption

A

’a characteristic that enhances the survival or reproduction of organisms that bear it, relative to alternative character states (especially the ancestral condition)’.

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5
Q

What was Lamarck’s theory

A

Inheritance of acquired characteristics

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6
Q

What is adaptive radiation

A

the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage

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7
Q

Example of adaptive radiation

A

Darwins finches - All arose from one ancestral species that colonized the Galapagos islands from S. America. Diverged into a large number of species within relatively short time. The lineages are modified for different ways of life. Differ in morphology of the bill – adaptation to different diets (seeds, insects, nectar etc)

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8
Q

What does natural selection act on

A

it acts on phenotypes, but selects for genotypes

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9
Q

What is directional selection

A

favours phenotypes of one extreme

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10
Q

What is diversifying ( or disruptive) selection

A

Favours the two extremes of a phentoype

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11
Q

What is stabilising selection

A

favours intermediate types and selects against extreme variants. Often leads to reduced phenotypic variation and status quo.

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12
Q

What is purifying selection

A

directional selection in favour of the prevalent, advantageous homozygous genotype. Removes mutations that change a phenotype

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13
Q

Example of stabilisng selection

A

Birth weight in humans (Cavalli-Sforza & Bodmer 1971)

Very heavy or very light babies were most likely to die

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14
Q

Why is selection on rare recessive alleles slow

A

most copies of the allele is in heterozygotes where the allele is hidden from selection

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15
Q

What is the best chance of removing a rare recessive allele

A

Best chance is that this goes to zero through drift – not selection!

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16
Q

Why are positive recessive alleles slow to increase initially

A

because mainly in ‘Aa’ Hz form - hidden from selection

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17
Q

What happens when a positive recessive allele becomes more common

A

it will increase rapidly once it has reached a certain frequency and eventually will go to fixation once past a certain initial frequency

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18
Q

3 ways variation is maintained

A

Mutations – (in the wider sense) - not all are deleterious
Gene flow – across different populations with different adaptations
Balancing selection – maintenance of greater variation than expected

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19
Q

2 mechanisms that make it hard to maintain variation

A

Selection and genetic drift

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20
Q

What 3 mechanisms can cause balancing selection

A

Heterozygote advantage
negative frequency dependent selection
Fluctuating selection

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21
Q

What is heterozygote advantage (over dominance

A

When the heterozygote has higher fitness than any of the homozygotes and so both alleles will be kept in the population in successive generations

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22
Q

What is negative frequency dependent selection

A

When the fitness of a genotype is not constant but depends on the genotype frequency in the population. in this case, the rarer the allele , the greater the advantage

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23
Q

What can negative frequency dependent selection lead too

A

Leads to oscillations in the phenotype frequency (and underlying alleles) in a population (maintains variation)

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24
Q

What are life history traits

A

affect the life table of an organism, and can be imagined as various investments in growth, reproduction, and survivorship.

25
Q

What are the disadvantages of sec

A

Halves the potential reproductive rate
Means you share your genetic reproduction
Break up co-adapted gene complexes
Cost of finding mates

26
Q

What are the advantages of sex

A

Stops the accumulation of deleterious mutations
Fisher- Muller hypothesis
Stops the accumulation of deleterious mutations
Fisher- Muller hypothesis

27
Q

What are the advantages of dispersal

A

Colonisation of new empty habitat
Inbreeding avoidance in sexual organisms
Find a ‘better’ environment

28
Q

What is dispersal

A

movement of organisms from location at birth to other locations where they breed

29
Q

What does natural selection select against alleles that promote dispersal

A

. Within a population there is automatic selection against dispersal alleles – they remove themselves from the population straight away!
Local adaptation – selection means that individuals are best suited to local conditions.
Offspring that disperse (and the dispersal allele) will end up in environments to which they are less well adapted – lower fitness
Dispersal is dangerous  higher mortality

30
Q

Examples of where organisms vary in life history/demographic traits

A 
Number and size of offspring
– Age distribution of reproduction
– Life span
– Alternative mating strategies
– Dispersal
– Mode of reproduction
31
Q

Example of variation in number size of offspring

A

Blue tits can lay 14 eggs whilst kiwis lay 1 which is 25% mothers weight

32
Q

Example of variation in the

A

Fruit flies live 26 days, Ming the icelandic clam llived 507 years

33
Q

In terms of r what is fitness

A

the per capita rate of increase of a genotype = r

34
Q

What will increase r (per capita rate of birth - per capita rate of death)

A

Higher survival up to and through the reproductive ages
Earlier age of first reproduction
Higher fecundity at each reproductive age
Higher fecundity early in life
Longer reproductive lifespan

35
Q

What don’t all organisms evolve traits that max out their fitness/r

A 
Phylogenetic constraints
Genetic constraints
Trade offs (e.g antagonistic pleiotropy)
36
Q

How can antagonistic pleiotropy affect fitness maximisation

A

due to allocation tradeoffs

  • genotypes differ in investment to reproduction or maintenance/growth
  • e.g increase fecundity but decreasein growth/survival
37
Q

What is senescence

A
  • physiological degeneration with age - increased likelihood of death
38
Q

What are theories of senescence based on

A

Based on the principle that
– due to extrinsic mortality less individuals survive / breed at older ages
– selective advantage of factors that enhance survival decreases with age

39
Q

Who are the people who gave the 2 main theories on senescence

A

Williams (1957)

Medewar (1952)

40
Q

What was Medewar (1952) theory about senescence

A

He argued that it was the accumulation of deleterious mutations that caused senescence - ie Medewar (1952) – accumulation of deleterious mutations
that only affect later age classes accumulate in populations
because selection against them is weak

41
Q

What was Williams (1957) theory on senescence

A

Because of greater contribution of earlier age classes to fitness, alleles that
provide an advantage in early life have a selective advantage… even if
deleterious later in life. ie antagonistic pleiotropy

42
Q

When is it an advantage ti be iteroparous

A
  1. If early age reproduction causes disproportionately high mortality - by investing more in early growth mortality may greatly reduce and lead to higher later fecundity
  2. Extrinsic mortality is low so enough time to repeatedly reproduce
  3. Population growth is low
43
Q

in terms of offspring number , what is the best fitness strategy

A

All else being equal, genotype with higher fecundity will have
higher fitness than one with lower fecundity.

44
Q

When are r-selected organisms better

A

In unstable or unpredictable environments with low density dependence, - the ability to reproduce quickly is crucial.

45
Q

When are k selected species better

A

In stable or predictable environments subject to strong density dependence, - ability to compete for limited resources is crucial

46
Q

Why are r and k selected strategies concept criticised

A

It’s polarised and does not

cover all the important elements of life-history theory

47
Q

What is anisogamy

A

difference in investment in sperm and eggs

48
Q

What is protogyny

A

– sequential hermaphroditism from female to male

49
Q

What is protandry

A

– sequential hermaphroditism from male to female

50
Q

What is sequential hermaphroditism associated with

A

Associated with changes in the relative reproductive success of the two sexes as an individual gets bigger

51
Q

What is heritability

A

The extent to which the variation of a trait within a population can be attributed to genetic factors

52
Q

What do you need to calculate heritability

A

You need phenotypic variance or you can’t calculate heritability , can’t divide by 0

53
Q

How do heritable affect the rate of change on a trait

A

Low heritabilities combine with strong selection
to produce change, but much more slowly
High heritabilities combine with strong
selection to produce rapid change

54
Q

Why is heriitabiity not the same as genetic determination

A

Heritability is a measure of what is associated with variation in a trait, not what causes a trait.

55
Q

Example of a trait with low heritability

A

Humans have 10 finger and toes because of genetics determine our body plant. Whilst some variation ca be explained genetically, most variation is explained by the environment

56
Q

Why is heritability not fixed

A

Heritability estimates are calculated for a given population, at a given time in certain environmental conditions.

57
Q

Why are studies on heritability in human behaviour difficult to conduct

A

People that share genetics also usually share environments
We can’t put clones of humans into controlled environmental conditions
We can’t separate children from their parents and do a regression analysis

58
Q

What is used to study heritability in human behaviour

A

Twin studies - is monozygotic twins resemble each other more on a certain trait than the dizygotic twins do, that trait is genetically
influenced

59
Q

What does heritability help us explain

A

Heritability helps us explain how much variation in a trait within a population can be attributed to genetic variation

Evolutionary Biology (7 decks)

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