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Biology > Evolution of Populations (Lecture 20) > Flashcards

Evolution of Populations (Lecture 20) Flashcards

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1
Q

Describe natural selection.

A

Natural selection is a process in which individuals with certain heritable characteristics survive and reproduce at a higher rate than others, resulting in differential success in reproduction - survival of the fittest.

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2
Q

Do individuals evolve from the process of natural selection?

A

No, individual members of a population only contribute to a population’s evolution - it is the population that evolves, not the individuals.

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3
Q

How does natural selection lead to the adaptation of a population to their environment.

A

Natural selection changes the gene pool of the population, gradually, over long periods of time. This either amplifies or diminishes only certain HERITABLE traits so that the population has the best chance of survival in their environment.

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4
Q

What is a population?

A

A population is a localized group of organisms of the same species.

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5
Q

What is a species?

A

A species is made up of individuals who have the potential to interbreed and produce viable, fertile offspring.

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6
Q

What is a gene pool?

A

A gene pool consists of all the genes in a population (all the alleles within that population).

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7
Q

Most species are diploid, meaning what?

A

Most species are diploid, meaning each locus is represented twice in an individual and that each individual is therefore either homozygous or heterozygous.

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8
Q

What is a fixed allele?

A

An allele for which all members of the population under study are homozygous, so that no other alleles for this locus exist in the population.

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9
Q

The Hardy Weinberg Principle states that the _____ of _____ and _____ in a ___-_____ population remain _____ (and this only applies to a simple __ _____ situation).

A

The Hardy Weinberg Principle states that the frequency of alleles and genotypes in a non-evolving population remain constant (and this only applies to a simple 2 allele situation).

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10
Q

What is the Hardy-Weinberg equation?

A

p^2 + 2pq + q^2 = 1, where p and q are the frequencies of two alleles.

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11
Q

The Hardy-Weinberg principle only holds true if the following 5 conditions are met:

Hint: The population cannot be evolving.

A

The situation is of a very large population. There is isolation from other populations (to avoid gene flow). There is no change in allele frequency due to mutations. There is only random mating (choice of partner is not influenced by genotype). No natural selection is occurring.

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12
Q

What is microevolution?

A

Microevolution is the change in the allele or genotype frequencies in a population from generation to generation.

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13
Q

What are the 5 primary causes of microevolution?

A

Genetic drift, natural selection, gene flow, mutations and nonrandom mating.

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14
Q

What are genetic drifts? What kind of populations do they occur in?

A

Genetic drifts are changes in the gene frequency as a product of chance and occurs only in small populations.

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15
Q

What are two causes of genetic drift?

A

The bottleneck effect and the founder effect are two causes of genetic drift.

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16
Q

What is the bottleneck effect?

A

The bottleneck effect occurs when disasters kill victims at random. The genetic makeup of the new (remaining) populations is not representative of the original. The bottleneck effect may reduce overall variability, meaning some alleles may be completely lost.

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17
Q

Describe the founder effect.

A

The founder effect occurs when a few individuals split from a population and colonize a new habitat. The genetic makeup of the new population is not representative of the original.

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18
Q

Under what condition does natural selection occur?

A

When individuals in a population are not equal in their ability to survive and produce viable, fertile offspring.

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19
Q

Give two examples of alleles that defend an organism being naturally selected.

A

Alleles that improve camouflage and mimicry are examples of defensive alleles that are naturally selected.

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20
Q

What are the two types of mimicry?

A

Batesian mimicry and Mullerian mimicry.

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21
Q

Describe Batesian mimicry.

A

Batesian mimicry is when a harmless species looks like a harmful one (like the viceroy butterflies that look like monarchs who taste bad).

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22
Q

Describe Mullerian mimicry.

A

Mullerian mimicry is when harmful species resemble each other, like the way bees and wasps have similar appearance.

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23
Q

List 3 factors that influence natural selection.

A

Competition for resources, reproductive survival and genetic variation.

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24
Q

What is the result of natural selection “selecting” the best alleles due to improved reproductive survival?

A

Natural selection eliminates unfavorable genotypes, thus producing genetic uniformity.

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25
Q

What are two mechanisms that preserve/restore genetic variation?

A

Diploidy (the state of being diploid) and and the heterozygote advantage.

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26
Q

How does diploidy preserve genetic variation?

A

Recessive alleles are not expressed in heterozygotes, meaning less favourable or harmful alleles may persist. This maintains a diverse pool of alleles which may be beneficial if conditions change by providing an advantage in that new environment.

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27
Q

How does the heterozygote’s advantage preserve genetic variation?

A

Relating to diploidy, heterozygotes are safe from fatal recessive genes. Still they are carriers who may pass it on, which also preserves genetic variation (mutations produce new alleles, sexual recombination).

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28
Q

What are the three types of natural selection?

A

Directional, stabilizing and diversifying.

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29
Q

Describe directional selection.

A

Directional selection occurs when the environment changes over time, thus favoring phenotypes closer to one of the extremes.

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30
Q

Provide an example of directional selection.

A

An example of this is antibiotic resistant bacteria, the alleles of which persist while non-resistant bacteria die.

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31
Q

Describe stabilizing selection.

A

Stabilizing selection occurs in a STABLE environment that favors the AVERAGE phenotype, meaning that extreme characteristics are selected against.

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32
Q

Provide an example of stabilizing selection.

A

An example is the fact that human birth weights of 3-4 kg are healthiest. Smaller or larger birth weights (extremes) have an increase in infant mortality rates.

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33
Q

Describe diversifying selection.

A

Diversifying selection occurs when EXTREME changes in the environment favor both EXTREME phenotypes.

34
Q

Provide an example of diversifying selection.

A

In a drought, birds with small beaks and birds with wider/longer beaks survive (extremes) while birds with average beaks perish.

35
Q

Diversifying selection is a _____ type of natural selection.

A

Diversifying selection is a disruptive type of natural selection.

36
Q

Describe gene flow.

A

Gene flow is when the migration of fertile individuals causes genes to flow between populations, thus reducing differences between populations.

37
Q

Describe mutations.

A

Mutations are a change in an organism’s DNA which immediately changes the gene pool. These are rare, unpredictable and spontaneous but they provide a continuous source of new alleles within a population. Not all mutations are helpful. Some don’t change anything and some can be harmful.

38
Q

What is non random mating?

A

Non random mating refers to mate selection based on one or more traits that are discriminated for or against.

39
Q

What is the effect of non random mating? How can this be detrimental to a population?

A

This results in an increase in the frequency of desirable traits, reducing genetic variation in a population. This can increase homozygosity of harmful alleles if they are present in the gene pool.

40
Q

Provide an example of non random mating and a consequence of it.

A

An example is in-breeding, which increases homozygosity.

41
Q

What are the 4 forms of evidence that support the theory of evolution?

A

Fossil records, comparative anatomy, comparative embryology and molecular biology.

42
Q

What 2 observations are supported from the 4 forms of evidence for the theory of evolution?

A

We observe that new species come from ancestral species and we observe an accumulation of modifications as a population adapts to a new environment.

43
Q

What do fossil records show?

A

They show the chronological appearance of a species, from their appearance to their extinction.

44
Q

Define comparative anatomy.

A

It is defined as anatomical similarities among species.

45
Q

What two types of evolution result in a comparative anatomy of two species?

A

Divergent and convergent evolution.

46
Q

Describe divergent evolution and the result of divergent evolution.

A

Divergent evolution is when a population becomes separated from the rest of the species. The different selection pressures result in different evolution patterns, yet there remains homologous structures between the (newly) different species.

47
Q

What are homologous structures?

A

Homologous structures originate from a common ancestor, but have adapted to different environments and even have different functions.

48
Q

Describe convergent evolution and the result of convergent evolution.

A

Convergent evolution is when different organisms occupy similar environments and so they evolve to resemble each other. These similarities between unrelated organisms are known as analogous structures.

49
Q

What are analogous structures?

A

Analogous structures resemble each other and even perform similar functions, but are not from common ancestry.

50
Q

What is comparative embryology?

A

This is when closely related organisms show similarities in their early stages of life (as embryos).

51
Q

Provide an example for comparative embryology.

A

For example, all chordates have pharyngeal slits at some point in their life cycle.

52
Q

What is molecular biology?

A

This is the observation of similarities/differences between organisms at the molecular level (DNA). The more closely related two species are, the higher the percentage of DNA and proteins that they have in common.

53
Q

Provide an example of molecular biology.

A

For example, humans and chimps share 98.8% DNA.

54
Q

What is macroevolution? What does it require?

A

It is the formation of a new species, which requires reproductive isolation to block genetic mixing from happening between different groups/species.

55
Q

What is reproductive isolation?

A

Reproductive isolation is essentially the block of gene flow between individuals of two different groups/species. It is not necessarily the physical isolation between two groups.

56
Q

What are the two types of reproductive isolation?

A

Prezygotic barriers and postzygotic barriers.

57
Q

What is a prezygotic barrier?

A

Prezygotic barriers are in place to prevent the formation of a zygote (before fertilization).

58
Q

What are the 5 types of prezygotic barriers?

A

Habitat isolation, behavioral isolation, temporal isolation, mechanical isolation and gamete isolation.

59
Q

Describe habitat isolation (prezygotic barrier).

A

Habitat isolation is when the habitat prevents species from encountering each other and mating.

60
Q

Provide an example of habitat isolation (prezygotic barrier).

A

There are two species of garter snakes; one that lives in water and another that lives on land. It is highly unlikely for the land snakes to mate with the water snakes due to localization.

61
Q

Describe behavioral isolation (prezygotic barrier).

A

This is the result of courtship rituals; species have specific signals and elaborate behaviour to attract mates, signals that other species would not recognize (or would be able to recreate) even if the two are closely related.

62
Q

Provide an example of behavioral isolation (prezygotic barrier).

A

An example is the meadowlark. The eastern and western meadowlarks are very similar to each other, but are different species. They don’t mate because of their different mating songs.

63
Q

Describe temporal isolation (prezygotic barrier).

A

This is when species that breed at different times of the day, during different seasons or different years cannot mix their gametes because they do not provide themselves with the opportunity to do so.

64
Q

Provide an example of temporal isolation (prezygotic barrier).

A

Brown and rainbow trout live in the same stream. However, since brown trout mate in the fall and rainbow trout mate in the spring, they never mate with one another.

65
Q

Describe mechanical isolation (prezygotic barrier).

A

This is when mating between closely related species is attempted but sperm transfer is prevented due to an anatomical incompatibility.

66
Q

Provide an example of mechanical isolation (prezygotic barrier).

A

When different species of snails attempt to mate, their genital openings are not aligned because their shells spiral in different directions.

67
Q

Describe gamete isolation (prezygotic barrier).

A

This is when the gametes of closely related species do not fuse, and so a zygote is not formed. Sperm transfer may be successful, but the gametes remain isolated from one another.

68
Q

Provide an example of gamete isolation (prezygotic barrier).

A

For example, the gametes of red and purple sea urchins cannot fuse with one another.

69
Q

What is a postzygotic barrier?

A

Despite prezygotic barriers, fertilization between two species may still occur. In this case, there are postzygotic barriers that contribute to reproductive isolation.

70
Q

What are the 3 types of postzygotic barriers?

A

Reduced hybrid viability, reduced hybrid fertility and hybrid breakdown.

71
Q

Describe reduced hybrid viability (postzygotic barrier).

A

This is when the hybrid does not complete development or does not live very long if it does complete its development.

72
Q

Describe reduced hybrid fertility (postzygotic barrier).

A

This is when hybrids are viable, but are sterile. This is because, during meiosis in a hybrid, they cannot produce normal gametes since the chromosomes of the parent species differ in number or in structure.

73
Q

Provide an example of reduced hybrid fertility (postzygotic barrier).

A

The cross between a donkey (62 chromosomes) and a horse (64 chromosomes) result is a viable mule that cannot produce normal gametes during meiosis (sterile).

74
Q

Describe hybrid breakdown (postzygotic barrier).

A

This is the final postzygotic barrier, which comes into play when the first generation offspring are viable and fertile. At this point, the following generation is feeble or sterile.

75
Q

What is speciation?

A

Speciation is the process from which new species arise from a preexisting species.

76
Q

What does speciation require?

A

It requires a block of gene flow; the separation of the gene pool from the parental population.

77
Q

Speciation can occur in two main ways, depending on how the gene flow is interrupted. What are they called?

A

There is allopatric speciation and sympatric speciation.

78
Q

Describe allopatric speciation.

A

This is when gene flow is interrupted by a population being divided into geographically isolated subpopulations. These geographical barriers may be caused by the emergence of mountain ranges, the movement of glaciers or the formation of land bridges

79
Q

Provide an example of allopatric speciation.

A

The grand canyon is impassable to small rodents. The result is that each rim has a unique species of rodents. Since the canyon is easily crossed by birds, there are the same species of birds on both rims.

80
Q

Describe sympatric speciation.

A

This is the formation of a new species within the parents population, meaning that reproductive isolation occurs without geographic isolation.

81
Q

Sympatric speciation occurs mostly in what type of organism? Why?

A

This occurs mostly in plants, when improper cell division causes plants to have an extra set of chromosomes (polyploidy).

82
Q

The terms “other country” and “same country” refer to _____ _____ and _____ _____, respectively.

A

The terms “other country” and “same country” refer to allopatric speciation and sympatric speciation, respectively.

Biology (12 decks)

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