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General Biology: OrganismL Biology and Evolution - Set 1 > Evolution of Populations > Flashcards

Evolution of Populations Flashcards

1
Q

What is a common misconception about evolution?

A

That individual organisms evolve - natural selection acts on individuals, but only populations evolve

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2
Q

What would happen to a population of medium found finches during a drought?

A

The large-beak birds are more likely to crack large seeds and survive - the finch population evolves, not its individual members

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3
Q

What makes evolution possible?

A

Genetic variation
Variation in heritable traits is prerequisite for evolution by natural selection
Phenotype is the product of inherited genotype and environmental influences
Natural selection can only act on variation with a genetic component

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4
Q

What can genetic variation be measured as?

A

Gene variability or nucleotide variability
For gene variability, average heterozygosity measures the average percent of loci that are heterozygous in a population

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5
Q

What does the site of nucleotide variation dictate?

A

The site of nucleotide variation dictates the likelihood of phenotypic variation
Differences occur in non coding regions (introns) less likely to have an effect
Variations that occur in coding regions (exons) ‘can’ change the amino acid sequences of the coded protein

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6
Q

What are the major sources of genetic variation?

A

Sexual reproduction can result in genetic variation by recombining existing alleles
New genes and alleles can arise by mutation or gene duplication

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7
Q

What three random sources create fresh assortments of existing alleles every generation?

A
  • crossing over
  • independent orientation of homologous chromosomes at metaphase 1 of meiosis
  • random fertilization
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8
Q

What serves as the raw material for evolution?

A

Mutations -creation of new alleles
- mutations are a “two-edged sword,” most being deleterious or neutral
- some mutations can be beneficial in instances when environment is changing such that mutations that were once disadvantageous are favorable under new conditions

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9
Q

What are the five main kinds of mutations?

A
  • point mutations
  • insertion / deletions (“indels”)
  • gene duplication
  • chromosome inversions
  • polyploidization
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10
Q

Point mutation

A

Single-base substitutions caused by DNA polymerase errors in either:
- DNA synthesis
- DNA repair
Often referred to as Single Nucleotide Polymerase or SNPs

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11
Q

What does redundancy in genetic code allow for?

A

It allows for silent mutations to persist

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12
Q

Silent mutations

A

Have no effect at all on the genetic code

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13
Q

Missense mutation

A

Change the amino acid coding, produces a different amino acid
Leads to a base substitution that produces an improved protein that enhances the success of the mutant organism and its descendant

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14
Q

Nonsense mutation

A

Changing of an amino acid into a stop codon

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15
Q

What can deletion/insertion mutations result in?

A
  • altering of the reading frame of the mRNA, so that nucleotides are grouped into different codons
  • lead to significant changes in amino acid sequence downstrene of the mutation
  • produce a nonfunctional polypeptide
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16
Q

A deletion

A

The loss of a chromosomal segment

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17
Q

A duplication

A

The repeat of a chromosome segment

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18
Q

An inversion

A

The reversal of a chromosome segment

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19
Q

A translocation

A

The attachment of a segment to a non homologous chromosome that can be reciprocal

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20
Q

Polyploidization

A
  • polyploid organisms have more than 2 sets of chromosomes
  • polyploidy usually occurs because of a failure in reduction division at meiosis which results in a 2n gamete
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21
Q

How do mutation rates vary across organisms?

A
  • mutation rates are low in animals and plants
  • the average is about one mutation in every 100,000 genes per generation
  • mutation rates are often lower in prokaryotes, but short generation time allow mutations to accumulate rapidly
  • viruses have both high mutation rates and short generation times - hence new flue vaccine every year
22
Q

What is the Lenski long-term evolution experiment?

A

The E. Coli long-term evolution experiment is an ongoing study in experimental evolution led by Richard Lenski that has been tracking genetic changes in 12 initially identical populations of asexual bacteria since 24 February 1988
The populations are now approaching 100,000 generations

23
Q

A population

A

A group of individuals of the same species, that live in the same area, and interbreed

24
Q

A gene pool

A

Consists of all the alleles for all loci in a population

25
Q

A locus

A

Fixed if all individuals in a population are homozygous for the same allele

26
Q

What happens if there are two or more alleles for a locus?

A

Diploid individuals may be either homologous or heterozygous

27
Q

How can we measure evolution?

A

We can measure evolution as a change i the prevalence of certain heritable traits in a population over a spa of generations

28
Q

Is there a change in the relative frequencies of alleles in a population over a number of generations?

A

Termed micro-evolution - evolution occurring on its smallest scale

29
Q

The Hardy-Weinberg principle

A

The shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population

30
Q

What does the Hardy-Weinberg equation describe?

A

The genetic makeup we expect for a population that is not evolving at a particular locus

31
Q

What does the observed frequencies not matching the expected suggest?

A

According to Hardy-Weinberg, it suggests that the population may be evolving

32
Q

What five conditions must be satisfied for a population to be in Hardy-Weinberg equilibrium?

A
  • a very large population
  • no gene flow between populations
  • no mutation
  • random mating
  • no natural selection
33
Q

What three major factors alter allele frequencies and bring about most evolutionary change?

A
  • natural selection
  • genetic drift
  • gene flow
34
Q

Natural selection

A

If individuals differ in their survival and reproduction success, natural selection will alter allele frequencies

35
Q

Random genetic drift

A
  • one Hardy-Weinberg assumption is that populations are a large size
  • in a process called genetic drift, chance events can cause allele frequencies to fluctuate unpredictably form one generation to the next
  • the smaller the population, the more impact genetic drift is likely to have
  • can result in maladaptive changes in allele frequency
36
Q

What can sampling errors do in finite populations?

A

They can alter allele frequencies in finite populations

37
Q

Founders effect

A

When a few individuals colonize an island or other new habitat
- the smaller the group, the less likely the genetic makeup of the colonists will represent the gene pool of the larger population they left

38
Q

Bottleneck effect

A

Occurs when there is a drastic reduction in population size due to a sudden change in the environment
- the resulting gene pool may no longer be reflective of the original population’s gene pool and results in genetic drift

39
Q

Gene flow

A
  • allele frequencies in a population can also change as a result of gene flow, where a population may gain to lose alleles when fertile individuals move into or out of a population or when gametes (such as plant pollen) are transferred between populations.
  • gene flow tends to reduce differences between populations
  • restrictions to gene flow tends to favor the formation of new species
40
Q

What mechanism consistently leads to adaptive evolution?

A

Natural selection is the only mechanism that consistently leads to adaptive evolution
- it’s only by chance that events such as genetic drift, gene flow, and mutations improve a populations fit or it’s environment
- some individuals are more likely than others to survive and reproduce
- natural selection is not random
- surviving individuals have a feared relative fitness - the contribution an individual makes to the gene. Pool of the next generation relative to others

41
Q

What are the three variations of ways natural selection and alter a population?

A
  • stabilizing selection
  • directional selection
  • disruptive selection
42
Q

Sexual selection

A

A form of natural selection in which individuals with certain characteristics are more likely than other individuals to obtain mares - can lead to sexual dimorphism

43
Q

Intrasexual sexual selection

A

Individuals of one sec compete for mates

44
Q

Intersexual selection

A

Mate choice

45
Q

What is the advantage to females of being chooses?

A

One hypothesis is that females prefer male traits that are correlated with “good genes”

46
Q

Trade offs for the male

A

Susceptibility to predators

47
Q

Why aren’t less adaptive alleles eliminated as the “best” alleles are passed to the next generation?

A

Natural selection acts on phenotype and so in diploid organisms recessive alleles can “hide” in heterozygous and be protected from natural selection

48
Q

Balancing selection

A

Occurs sub natural selection maintains stable frequencies of two or more phenotypic forms in a population
- example: Heterozygous advantage - heterozygotes have greater success than either homozygote

49
Q

Frequency- dependent selection

A

Acts against either phenotype if it becomes too common

50
Q

What are the four “better than” basis’ of evolution?

A
  • selection can act only on existing variations. New, advantageous alleles do not arise on demand
  • evolution is limited by historical constraints. Evolution co-opts existing structures and adapts them to new situations
  • adaptations are often compromises. Specialization in one trait often has costs
  • chance, natural selection, and the environment interact. Environments often change unpredictably

General Biology: OrganismL Biology and Evolution - Set 1 (23 decks)

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