Lec 11 slides and reading Flashcards

1
Q

how can complex adaptations evolve?

A

In the evolution of organisms and their complex machinery, many aspects are modified (adapted) versions of pre-existing structures
Just as in biological evolution, many early designs were developed that seem poor by today’s standards, yet each one was an improvement on the ones before
In natural evolution, it results from what has been called ‘tinkering’ with the organism, with minor changes that make their possessors survive or reproduce better than others
In the evolution of a complex structure, several traits must evolve simultaneously, so that the different parts of the structure are well adapted to function as a whole
After enough time, the structure will differ from its ancestral state in many different ways, so that individuals in the descendant population have combinations of characteristics never seen in the ancestral population

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2
Q

example of adaptation evolving

A

An organism that could change a similar chemical into the useful one would benefit, and so an enzyme could evolve to catalyze that change
The useful chemical would now be synthesized from the related one
Thus, a short biosynthetic pathway, with a precursor and a product, would be favoured

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3
Q

2 sources of evidence of complex adaptations evolving in steps

A

-existence of intermediates in the fossil record
-present day species that show intermediate stages b/w simple and more advanced stages

In many cases, there is a complete absence of intermediates. E.g. the major divisions of multi-cellular animals(molluscs, arthropods, and vertebrates) nearly all appeared suddenly in the Cambrian with no fossil evidence concerning their ancestors
Recent DNA sequence studies of the relationships between them suggest strongly that these groups were already separate lineages long before the Cambrian era (we don’t know what they look like since they’re soft-bodied→ unlikely to fossilize)

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4
Q

evidence on features that don’t fossilize

A

Example provided by flight
No fossils connecting bats with other mammals, the first bat fossils, found in deposits over 60myo, have the same highly modified limbs as modern bats
Species that can glide evolve to have similar body structure to bats with wings
Similar to evolution of eyes
All vertebrate animals have the same design of eye, but with many variations of detail adapted to different modes of life
Many types of invertebrates have simple eyes, with no lens and don’t need to see clearly

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5
Q

why do we age?

A

To measure aging, we can study many individuals kept in a protected environment, where ‘external’ causes of mortality such as predation have been removed, so that individuals live for much longer than in nature
This increase in mortality reflects the deterioration of multiple biological functions with advancing age: almost everything seems to get worse, from muscular strength to mental ability
Aging is an unavoidable consequence of cumulative damage to the systems necessary for continued survival, and selection probably can’t prevent this
Single-celled organisms reproduce by dividing into daughter cells but don’t senesce(grow old), they continually break down damaged components and replace them with new ones
They continue to propagate(reproduce) indefinitely, provided that harmful mutations are removed by selection

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6
Q

evolutionary explanation of aging

A

These species differences indicate that aging evolves and therefore demands an evolutionary explanation
Selection favours survival and reproduction early rather than late in life since more individuals will be alive to experience the good effects
Aging evolves because of the greater selective value of variants with favorable effects on survival or fertility early in life, compared with variants that act late

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7
Q

2 main ways in which natural selection might work to cause aging:

A

Mutations with harmful effects will be most strongly selected against if they express their effects early in life

1st way: selection keeps early-acting mutations rare in populations, while allowing ones with effects late in life to become common
-many common human genetic diseases are due to mutations whose harmful effects appear late in life (Alzheimer’s disease)

2nd way: variants that have beneficial effects early in life will be more likely to spread through the population than those whose good effects come only in old age
-improvements to the early stages of life can evolve, even if these benefits come at the expense of harmful side effects later on
-e.g. higher levels of some reproductive hormones may enhance women’s fertility early in life, but at the risk of later breast and ovarian cancer

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8
Q

what does ev. theory predict about species with low death rates

A

Evolutionary theory of aging predicts that species with low externally caused death rates should evolve low rates of aging and longer life-spans, compared with species with higher external death rates
Strong relation between body size and the rate of aging, smaller species of animals tending to age faster than larger ones, and to reproduce earlier
This reflects the greater vulnerability of many small animals to accidents and predation

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9
Q

how are we an example of evolution of a slower rate of aging

A

Our closest relatives, chimpanzees, rarely live past 50 years in captivity and start reproducing earlier in life than humans
Humans have therefore substantially reduced their rate of aging since diverging from our common ancestor with apes, and postponed reproductive maturity
These changes are probably due to increased intelligence and ability to cooperate, which reduced vulnerability to external causes of death and reduced the advantage of reproducing early

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10
Q

how has industrialization led to a decline in mortality rates

A

Industrialization has led to a dramatic decline in mortality rates among adults, which is evident in census data
This changes the natural selection affecting the aging process in human populations

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11
Q

huntington’s disease and frequency of mutant genes

A

In industrialized societies, with low mortality, people quite often have children at ages when the disease could appear, and in consequence, affected people have on average 15% fewer children than unaffected individuals

If current conditions continue, selection will gradually reduce the frequencies of mutant genes with effects expressed late in reproductive life, and the survival rates of older individuals will increase

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12
Q

evolution of sterile social castes

A

Another problem for evolutionary theory is posed by the existence of sterile individuals in a number of types of social animals
In social wasps, bees and ants, some of the females in a nest are workers, who do not reproduce
Reproductive females are a small minority within the colony (often just a single queen); the worker females look after the queens’ offspring and maintain and provide for the nest
In the other main group of social insects, the termites, both males and female can behave as workers
In the advanced social insects, there are often several different ‘castes’, which perform very different roles and are distinguished by differences in behavior, size and body structure

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13
Q

kin selection

A

The members of a social group (e.g. naked mole rat) are generally close relatives, often sharing the same mother and father (concept of kin selection)

A genetic variant that causes its carriers to forgo their own reproductive success to help raise its relatives may help the relatives’ genes pass to the next gen and the relatives’ genes are often the same (bc of relatedness) as the helper individual’s own genes (in the case of a brother/sister, if one individual has a genetic variant inherited from one parent, the chance is one-half that the variant will be present in the other)

If the sacrifice by sterile individuals results in a sufficient increase in number of surviving and reproductively successful relatives, the increase in number of copies of the ‘worker gene’ can outweigh the decrease due to their own lost reproductive success

The increase needed to outweigh the loss is smaller the closer the degree of relationship

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14
Q

what does kin selection provide a framework for

A

This principle of kin selection provides a framework for understanding the origins of sterility in social animals
Accounts for many details of animal societies, including those with less extreme features than sterile castes
E.g. in some bird species, juvenile males don’t attempt to mate, but remain as ‘helpers’ at their parental nest while younger siblings are being cared for

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15
Q

If a colony with soldiers is better defended against enemies, and if colonies with the variant can produce more reproductives on average, the variant will _______ the success of its colony

A

increase

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16
Q

If the reproductively active members of the colony are close relatives of the workers, the genetic variant that induces some workers to become soldiers will be transmited by the colony via queens and males founding new colonies

Selection can thus act to ________ the representation of this variant among colonies in the species

A

increase

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17
Q

The origin of living cells and the origin of human consciousness

A

Consciousness is a matter of degree, so that in principle there is little difficulty in imagining a gradual intensification of self-awareness and ability to communicate during the evolution of our ancestors

Mutations have been found which lead to deficiencies in specific aspects of speech of their carriers, leading to identification of a gene involved in the control by the brain of some aspects of speech

18
Q

many changes in DNA sequences have little or no effect on the functioning of the organism, so that evolutionary changes in sequences can occur by …

A

the random process of genetic drift

19
Q

The tech of DNA sequencing enables us to study variation and evolution at the level of the genetic material itself, and to use ________ ________ to reconstruct the genealogical relationships between species

A

sequence differences

20
Q

This knowledge of heredity and our understanding that natural selection drives the _____ of organisms’ physical and behavioural characteristics, doesn’t imply rigid genetic determination of all aspects of such characteristics

A

evolution

21
Q

Natural selection merely accumulates __________ that are favourable under prevailing conditions

A

variants

22
Q

what is the ‘unit of selection’

A

-there is variation among units at that level
-units exhibit heritability across gens
-units have differentiable fitness (survival and/or reproduction)

23
Q

target of selection

A

the gene
-units of inheritance

24
Q

how does multi-level selection pose a problem for complexity

A

-selection at a given level of organization means that units compete to maximize fitness
(operating at different levels is a problem)
-competition among lower level units of organization may reduce fitness at higher levels

25
Q

how can higher-level fitness costs be avoided

A

if lower level units of organization cooperate rather than compete

26
Q

how do biological subunits stay so cooperative

A

many features of individual organisms prevent competition within an individual
-prevents evolution within individuals
-align fitness interests across levels of
organization

ensures that many genes succeed by enhancing the fitness of the individual

27
Q

2 ways that biological subunits stay cooperative

A

1) mitosis and meiosis
-ensures that alleles don’t compete within an individual
-fair representation of gene variants among daughter cells

2) development and multicellularity
-starting from a single cell prevents initial competition among cell lineages

28
Q

positive natural selection on alleles

A

alleles spread through a population by increasing individual fitness

29
Q

how do genomes stay cooperative?

A

1) fair meiosis
-meiosis provides a fair representation of an allele’s fitness effects on individuals

30
Q

meiotic drive

A

when alleles get out of line

if an allele can bias its own transmission
-then it can spread to higher frequency
-even while reducing individual fitness
-“selfish” genetic element relative to organism’s fitness interests

-violation of mendel’s laws and causes evolution to go in wrong direction

31
Q

during meiotic drive, by enhancing its own transmission, meiotic drive allele (a) can spread _________ of (a) even while REDUCING individual fitness

A

increased frequency

32
Q

meiotic drive can rapidly eliminate individuals that have ______ individual fitness

A

higher

33
Q

what’s the evolutionary response to cheating?

A

when cheating alleles spread, there’s strong selection on rest of genomes for suppression of cheating

34
Q

transposable elements: cheating mendel’s laws through over-replication

A

-TE’s are self-replicating segments of DNA (aka transposons)
-jumping gene (makes copies of themselves and insert into gene)
-TE replication separated from cellular replication
-ensure their own over-representation in offspring

35
Q

first way how genomes don’t ‘explode’ from transposition?

A

1) alleles arising elsewhere in genomes that SILENCE TEs will be favoured by individual selection
-mechanisms controlling DNA and histone methylation
-piRNAs and RNA interference may have evolved as silencing mechanisms

36
Q

second way how genomes don’t ‘explode’ from transposition?

A

transposition-selection balance
-transposition is a form of mutation that can disrupt a gene
-NS against harmful effects on the organism reduces abundance of chromosome copies with most TEs
-abundance of TEs in an organism results from a balance between these opposing forces

37
Q

how do individual genomes stay so cooperative

A

-many features ensure that the variance in fitness WITHIN an individual is minimized
-ensures that many genes succeed by enhancing the fitness of the organism
-presence of strong selection on rest of genome seems essential to maintain higher-level of cohesion

38
Q

how do collections of cells stay cooperative?

A

1) starting from a single cell reduces competition within individuals
2) separation of germline with limited numbers of cell divisions inhibits transmission of selfish cell lineages
3) tumor suppressors, other features inhibit unregulated cell division (minimizes in gene line)

39
Q

what’s the problem with somatic mutation in mc organisms

A

-somatic mutations might be selectively favoured within an individual
-creates selection for cancers

40
Q

cancer

A

spreads commonly in tissue that’s relatively undifferentiated
-evolves resistance to treatment/immune system

illustrates the “short-sightedness” of the evolutionary process