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Bio > Population Genetics > Flashcards

Population Genetics Flashcards

1
Q

What is a population?

A

A group of the same species living in a specific environment/area

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2
Q

What is microevolution?

A

The change in allelic frequencies in a population over time

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3
Q

Natural selection works on ________, evolution works on __________, and the ____________

A

Individuals
Populations
alleles they collectively carry

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4
Q

Describe nonheritable variation

A

The environment influencing phenotype

ex. the caterpillars have different appearances because of the chemicals in their diets, not because of different genotypes

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5
Q

________ causes phenotypic variation based on changes in genes/DNA sequences

A

Genetic variation

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6
Q

What are the sources of genetic variation?

A

New alleles arising through mutations (changes in DNA sequence)
- can be harmful, or masked in the heterozygote

Heritable changes in germline cells, non-heritable in somatic cells
- errors in meiosis during gametogenesis

Spontaneous mutations through errors in DNA replication

Induced mutations through exposure to mutagens (radiation, etc.)

Sexual reproduction during crossing over, independent assortment, and random fertilization

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7
Q

Point mutations in introns result in _________ variation

A

neutral

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8
Q

What does the gene pool consist of?

A

All copies of every type of allele at every locus in all members of a population

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9
Q

When does a fixed allele occur?

A

When there is only one allele for a particular locus in a population (all individuals are homozygous for that trait)

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10
Q

What are the conditions for Hardy-Weinberg equilibrium

A

no mutations (alleles stay the same)

Random mating

No natural selection (neither trait has an advantage)

Large population (no genetic drift)

Isolated Population (no gene flow)

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11
Q

What is genetic drift?

A

Occurs in small populations - can cause an allele to be disproportionately over-underrepresented in the next generation (the smaller the population the bigger the effect)

Through chance alone, the frequency of alleles can shift around (not dependent on the environment).

Can lead to a loss of genetic variation within populations. Alleles can even be lost in the population.

Can cause harmful alleles to become fixed

*NOT natural selection

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12
Q

What is the bottle neck effect?

A
  • an example of genetic drift

a sudden change in the environment randomly kills a large number of individuals

this can drastically alter the allele frequency in the remaining population - random which individuals die and which survive (not natural selection)

They pretty much always reduce the allele variability in the surviving population

Genetic drift can readily occur in the surviving population

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13
Q

What is the Founder effect?

A

*example of genetic drift

When a group of individuals (and their alleles) move to a new area and form a new population
- original population where they came from still exists

This can account for many certain inherited disorders in humans (British colonists move to island and one was homo recessive for blindness so now the rate is 10x higher)

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14
Q

What is gene flow?

A

Transfer of alleles into or out of population due to the movement of fertile individuals or their gametes

Reduces genetic differences between populations because alleles are exchanged

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15
Q

Describe directional selection

A

Shifts the overall makeup of the population by favouring variants that are at one extreme of the phenotypic distribution

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16
Q

What is disruptive selection?

A

Favours variants at both ends of the phenotypic extreme

17
Q

What is stabilising selection?

A

removes the extreme phenotypic variations from the population and preserves the intermediate types
ex. human babies birth weight

18
Q

What is sexual selection, what can it result in, and what are the two different types?

A

individuals with certain inherited traits are more likely than others to obtain mates

can result in sexual dimorphism -> differences in secondary sexual characteristics between males and females of the same species (ex. bigger males and small females)

InTRAsexual selection = selection within the same sex where individuals compete directly for mates of the opposite sex

inTERsexual selection = “mate choice” individuals in one sex are choosy in selecting mates
- ex. blue footed boobies with their blue feet

19
Q

What is balancing selection? What are the two examples of this?

A

maintains two or more phenotypic forms in a population

- frequency-dependent selection = the fitness of a phenotype depends on how common it is in the population  ex. right and left mouthed fish
  • heterozygote advantage = heterozygous individuals have great relative fitness than either of the homozygous individuals
    ex. sickle cell disease and malaria resistance
20
Q

What happens each time a species splits (speciation)?

A

The new species share characteristics of the common ancestor -> homologous structures and divergent evolution

New genes, mutations leading to new alleles, and natural selection can mold new traits in the new species giving rise to biological diversity -> can result in analogous structures and convergent evolution

The two species can then later split into other new species

21
Q

We now think that there are ______ eukaryotic species alive now

There may be as many as ______ extinct species

A

8.5 million

5 billion

22
Q

What is macroevolution?

A

The broad pattern of evolution above the species level

23
Q

What are the three concepts by which we define a species?

A

Biological species concept

Morphological species

Ecological species concept

24
Q

Describe the biological species concept
What’s the problem with this concept?

A

A species is a group of populations whose members have the potential to interbreed in nature and produce fertile offspring
- organisms must reproduce sexually for this definition to work
- must be able to see successful reproduction (*doesn’t work with the fossil record)
- formation of new species depends on reproductive isolation (no gene flow)

Problem: Can be a little fuzzy since sometimes hybrids can occur (two species mate)

25
Q

Describe the morphological species concept
What’s the problem with this?

A

Classifications of species based upon physical traits such as size, shape, or other features of morphology
- no observation of breeding needed
- can use organisms with observation data (museum records)
- can be used for the fossil record
- can lead to false classifications

  • some species have a lot of morphological variation (dogs)
26
Q

Describe the ecological species concept?

A

Views a species in terms of its ecological niche, the sum of how members of the species interact with the nonliving and living things within its environment
- ex. oak trees where one is more tolerant to dry, and the other is not
- can accommodate asexual and sexual species
- emphasizes disruptive selection as organisms adapt to different environments

27
Q

What are the 2 different groups of reproductive barriers?

A
  1. Prezygotic barriers - prevents mating or fertilization between species
  2. Postzygotic barriers - operate after hybrid zygotes are formed
28
Q

Describe habitat isolation

A

Two species that occupy different habitats within the same area may encounter each other rarely, even though they are not separated by obvious physical barriers (ex. mountains)
- ex. the apple maggot fly eats apples and the blueberry maggot fly eats blueberries even in the same geographic range

29
Q

Describe temporal isolation (prezygotic barrier type)

A

Species that breed at different time in the day, different season, or different years cannot mix their gametes

30
Q

Describe behavioural isolation (prezygotic barrier type)

A

Different courtship rituals

Species have different behaviours that are not preferred by individuals of other species
- enables mate recognition

31
Q

Describe mechanical isolation (prezygotic barrier type)

A

Physical incompatibility of reproductive parts

  • mating is attempted, but morphological differences prevent its successful completion
32
Q

Describe gametic isolation (prezygotic barrier type)

A

Molecular incompatibility of eggs and sperm

  • mating is attempted, but molecular differences prevent its successful completion
  • sperm of one species might not be able to fertilize the egg of another
33
Q

What are the two kinds of postzygotic barrier types?

A

Reduced hybrid viability, development, or survival -> hybrids do not develop fully or are unable to reproduce due to interaction of parental genes OR hybrids may be healthy but they are sterile and can’t reproduce

Hybrid breakdown -> some first-generation hybrids are fertile and viable, but when they breed with one another or with the parental species, the F2 generation are feeble or sterile

34
Q

What is allopatric speciation?

A

When a population is divided into geographically isolated populations due to changes in geography or waterbodies
- a geographic barrier separates two populations of the same species, restricting gene flow

Often when the population is small it can lead to the founder effect or genetic drift

Differential environmental pressures between the two locations can trigger natural selection

*eventually the two populations are so different genetically that reproductive barriers arise between them, forming separate species

35
Q

What is sympatric speciation?

A

When a population is divided WITHOUT geographic isolation
- can arise through polypoidy, habitat differentiation or sexual selection

36
Q

What is polyploidy, autoploidy, and allopolyploidy??

A

Poly -> cells/organisms contain more than two paired (homologous) sets of chromosomes (more than 2n

Auto -> doubling of chromosomes in the same species (most common in plants)

Allo -> hybridization of two different species, followed by cell division error (many important crops are caused by allopolyploidy)

37
Q

What is habitat differentiation?

A

When a subpopulation of a species start to exploit a habitat or resource not used by the parent population
ex. apple maggot flies normally eat hawthorns but a bunch started to eat apples and apples mature earlier than hawthorns so temporal reproductive barrier happening

38
Q

How does sexual selection occur allopatrically and sympatrically?

A

Allo -> separated populations develop new mating behaviours and thus will not interbreed with the original population if re-introduced

Sympatric -> changing in mating behaviours in the same habitat led to restrictions in gene flow leading to speciation over time

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