Mechanisms of Evolution: Selection, Genetic Drift, and Mutations

70 practice flashcards in Question and Answer style covering the mechanisms of evolution including selection pressures, natural, sexual, artificial selection, genetic drift, and mutation based on lecture notes.

What are selection pressures?

External agents that affect an organism's ability to survive in a given environment.

How is a selection pressure classified if it decreases the occurrence of a trait?

It is a negative selection pressure.

How is a selection pressure classified if it increases the proportion of a trait?

It is a positive selection pressure.

Why might the definition of a beneficial adaptation change over time?

Because selection pressures may not remain constant.

What factors are included under 'resource availability' selection pressures?

Food, habitat (shelter / territory), and mates.

What environmental conditions can act as selection pressures?

Temperature, weather conditions, or geographical access.

Which biological factors are identified as selection pressures?

Predators and pathogens (diseases).

What is the primary effect of natural selection on characteristic frequency?

It increases the frequency of characteristics that make individuals better adapted and decreases the frequency of others.

What determines the direction of phenotypic change in a species?

The selection pressure.

Where is the island of Daphne Major located?

In the Galapagos archipelago.

During what years was the drought on Daphne Major observed?

From $1976$ to $1978$.

What change occurred in vegetation on Daphne Major during the extended drought?

Plants produced larger, tougher seeds.

How did finch populations on Daphne Major respond to the production of larger, tougher seeds?

Finches with larger beaks were better equipped to feed and produced more offspring with larger beaks.

Define sexual selection.

A type of selection where a particular trait provides greater success in obtaining mates and reproducing.

Can sexual selection traits be counterproductive to survival?

Yes; for example, bright plumage in birds makes them more visible to predators.

What is the result of sexual selection on mating patterns?

It leads to non-random mating, where not all individuals have equal opportunities to pass on alleles.

What biological family do birds-of-paradise belong to?

The family Paradisaeidae.

What term describes the distinct appearance differences between males and females in birds-of-paradise?

Sexually dimorphic.

Where do elaborate feathers typically extend from on male birds-of-paradise?

The beak, wings, tail, or head.

Which two selection types influence the characteristics of guppies?

Natural selection and sexual selection.

Why do guppies living near predators exhibit drab colouration?

Because of natural selection for better camouflage and survival.

Why do guppies in predator-free regions have brighter colours?

Because of sexual selection, as they are preferred by females.

Who is the Canadian biologist known for guppy modeling experiments?

John Endler.

What occurred when drab guppies were moved to a region free of predators?

The population rapidly evolved to favour brightly coloured male fish.

What selection pressure was demonstrated by John Endler's guppy experiment?

The significance of predatory fish as a selection pressure.

What is artificial selection?

The identification by humans of desirable traits in plants and animals and the steps taken to enhance them in future generations.

What are the three categories of selection based on phenotype distribution effect?

Stabilising selection, directional selection, and disruptive selection.

What happens in stabilising selection?

An intermediate phenotype is selected for, and extremes are selected against.

What is a classic human example of stabilising selection?

Human birth weight.

Why are extreme birth weights in humans selected against?

Lower and higher birth weights are linked with increased infant mortality.

Define directional selection.

A type of selection where one extreme of the phenotype range is selected for.

Which organism is a famous example of directional selection following the industrial revolution?

The peppered moth.

Why did lighter moths have a survival advantage pre-industrial revolution?

The environment was unpolluted and had lighter coloured surfaces like tree bark and lichen.

Why did darker moths gain a survival advantage after the industrial revolution?

The environment became heavily polluted, darkening surfaces.

How are recent environmental policies in Europe affecting peppered moth populations?

By reducing pollution levels, they are altering the frequency of the two populations again.

What is disruptive selection?

Selection that favours individuals with the smallest and largest values of a trait, while intermediate values are at a disadvantage.

What bird species demonstrates disruptive selection regarding plumage?

Lazuli buntings.

Which male lazuli buntings are able to establish territories and breed?

Only those that are brightly coloured or dull.

Which lazuli buntings do not mate?

Males with intermediate plumage.

Which two types of selection lead to speciation over the long term?

Directional selection and disruptive selection.

How does stabilising selection affect the mean phenotype over long periods?

It maintains the existing type without changes in the mean phenotype.

What happens to the frequency of genetic variants underlying reproductively successful phenotypes?

They increase in frequency over time.

Genetic changes across generations result from differences in what?

Reproductive success of genetically determined phenotypes.

What is the primary source of all new alleles?

Mutations.

How can mutations change the frequency of existing alleles?

By competing with them.

Under what condition may recurrent spontaneous mutations become common?

If they are not harmful and are not eliminated.

In the provided selection graph, which allele is created by a mutation?

The recessive allele $a'$.

When does the frequency of allele $a'$ increase in the mutation model?

When environmental conditions change, giving it a competitive advantage over allele $a$.

What is genetic drift?

Random changes in gene frequencies in a gene pool due to random chance.

What are the two possible outcomes for alleles due to genetic drift?

They may become lost or fixed (present in all individuals).

In what size of population is genetic drift most significant?

Small populations.

Does genetic drift work to produce adaptations?

No; it is a mechanism of evolution but does not work like selection pressure to produce adaptations.

What defines a population bottleneck?

An event that reduces population size by an order of magnitude, specifically $> 50 \%$.

What can cause population bottlenecks?

Natural occurrences (fires, floods) or human induction (overhunting).

How does genetic variability in a post-bottleneck population compare to the original?

The surviving population has less genetic variability.

What happens to the gene pool as surviving bottleneck members repopulate?

The newly developing gene pool will be divergent to the original.

When did cheetahs narrowly escape extinction during the last ice age?

Between $10,000$ and $20,000$ years ago.

From what small group are all modern cheetahs thought to have arisen?

A single surviving litter.

What sperm issue is caused by the lack of genetic variation in cheetahs?

Sperm abnormalities.

What term describes the decreased female fertility found in cheetahs?

Decreased fecundity.

List two survival-related consequences of the cheetah bottleneck.

High cub mortality and sensitivity to disease.

Why has genetic variation not returned to cheetah populations?

There has been insufficient time for random mutations to produce new variation.

What is the founder effect?

When a small group breaks away from a larger population to colonise a new territory.

Why might a founder group's gene pool be non-representative of the parent population?

Due to random chance in the sample of alleles taken by the small group.

As a founder colony increases in size, what happens to its gene pool representation?

It will no longer be representative of the original gene pool.

How does the founder effect differ from a population bottleneck?

In the founder effect, the original population remains largely intact.

When is coevolution likely to occur?

When different species have close ecological interactions with one another.

What are three examples of ecological relationships involving coevolution?

Predator/prey and parasite/host; competitive species; and mutualistic species.

What is the course title for the lecture notes provided?

BIO$5$ Continuity of Life on Earth and Homeostatic Systems.