AH Biology - Unit 2 - KA2(a) - Drift and Selection

What is evolution?

Evolution is the change over time in the proportion of individuals differing in one or more inherited traits.

What happens to allele frequency during evolution?

During evolution, there are changes to the allele frequency in the population (how common different alleles are in a population).

What three key mechanisms do changes in allele frequency occur through?

The three key mechanisms that changes in allele frequency occur through are:

• Natural selection

• Sexual selection

• Genetic drift

What are the two non-random key mechanisms that cause changes in allele frequency?

The two non-random key mechanisms that cause changes in allele frequency are:

• Natural selection

• Sexual selection

What is the random key mechanism that causes changes in allele frequency?

The random key mechanism that causes changes in allele frequency is genetic drift.

Is natural selection a non-random or random mechanism?

Natural selection is a non-random mechanism.

Is sexual selection a non-random or random mechanism?

Sexual selection is a non-random mechanism.

Is genetic drift a non-random or random mechanism?

Genetic drift is a random mechanism.

What is natural selection?

Natural selection is the non-random increase in the frequency of DNA sequences (alleles), that increase the organisms survival chances.

What is required for natural selection to occur?

Natural selection can only occur in populations that show genetic variation.

What does genetic variation in a population arise as a result of?

Genetic variation in a population arises as a result of mutations.

What are mutations?

Mutations are the original source of new DNA sequences. These new sequences can be new alleles.

What are mutations normally and what can occasionally arise?

Normally, mutations are harmful or neutral. Occasionally beneficial alleles arise that increase an individuals fitness.

What are the stages of natural selection?

The stages of natural selection are:

1. Mutations arise and produce new alleles

2. Populations produce more offspring than the environment can support. This creates a selection pressure that means not all individuals will survive.

3. Individuals that are better suited to their environment tend to survive longer and can produce more offspring.

4. These individuals breed and pass on their advantageous alleles to the next generation.

What is stage 1 of natural selection?

Stage 1 of natural selection is “Mutations arise and produce new alleles”

What is stage 2 of natural selection?

Stage 2 of natural selection is “Populations produce more offspring than the environment can support. This creates a selection pressure that means not all individuals will survive.”

What is stage 3 of natural selection?

Stage 3 of natural selection is “Individuals that are better suited to their environment tend to survive longer and can produce more offspring.”

What is stage 4 of natural selection?

Stages 4 of natural selection is “These individuals breed and pass on their advantageous alleles to the next generation.”

What happens over time due to natural selection?

Over time, these advantageous alleles become more frequent in the population through inheritance.

What does natural selection result in?

Natural selection results in the non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles.

What is sexual selection?

Sexual selection is the non-random process involving the selection of alleles that increase the individuals chances of mating and producing offspring.

What do alleles selected by sexual selection not help?

Alleles selected by sexual selection do not help organisms survive.

What two key processes is sexual selection driven by?

The two key processes sexual selection is driven by are:

• Male to male rivalry

• Female choicd

What is male to male rivalry?

Male to male rivalry is a process where males are selected for larger body size or weaponry. These use these to increase their access to females through conflict. Examples of features selected for are antlers or horns.

What is female selection?

Female selection is a process where females use honest signals such as tail feather length or bright plumage to assess male fitness and male parasite burden. Females are more likely to mate with fitter males who have less parasites. Generally, females invest more in their offspring, so are more selective of mates than males. (Quality over quantity)

What is sexual dimorphism?

Sexual dimorphism is when makes and females of a species look different to each other. Normally males have a larger size and are more conspicuous. Females will often look inconspicuous to camouflage from predators while sitting on the nest or caring for young.

What is sexual dimorphism driven by?

Sexual dimorphism is driven by sexual selection.

When does genetic drift occur?

Genetic drift occurs when chance events cause unpredictable changes in allele frequencies from one generation to the next.

Is genetic drift a random or non-random process?

Genetic drift is a random process.

In what size of population is genetic drift more important in?

Genetic drift is more important in small populations because alleles are more likely to be lost from the populations gene pool (all of the alleles present in the population)

As a result of genetic drift, what can happen to certain alleles?

As a result of genetic drift, certain alleles in the gene pool may be over-represented or under-represented in the next generation.

What are the two key processes that can occur during genetic drift?

The two key processes that can occur during genetic drift are:

• The founder effect

• The bottleneck effect

What is the founder effect?

The founder effect is when a few members are isolated from a larger population. The gene pool does not represent that of the original population.

What is the bottleneck effect?

The bottleneck effect is when a bottleneck occurs and the population size is reduced for at least one generation. This is often the result of a natural disaster. The gene pool of the new population does not represent that of the original one.

What are selection pressures?

Selection pressures are environmental factors that influence which individuals in a population pass on their alleles.

When selection pressures are strong, what is the rate of evolution?

When selection pressures are strong, the rate of evolution can be rapid.

What are examples of biotic selection pressures?

Examples of biotic selection pressures are:

• Competition

• Disease

• Predation

• Parasitism

What are examples of abiotic selection pressures?

Examples of abiotic selection pressures are:

• Temperature

• p.H

• Light

• Humidity

• Salinity

What does the Hardy-Weinberg principle state?

The Hardy-Weinberg principle states that in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over generations.

What are conditions that maintain the Hardy-Weinberg equilibrium?

Conditions that maintain the Hardy-Weinberg equilibrium are:

• No natural selection

• Random mating (Therefore no sexual selection)

• No mutations (Therefore no new alleles)

• Large population size (Therefore genetic drift has no effect)

• No gene flow (No migration)

What are the two equations in the Hardy-Weinberg principle?

The two equations in the Hardy-Weinberg principle are:

• p²+2pq+q²=1

• p+q=1

What does p² represent in the Hardy-Weinberg principle?

In the Hardy-Weinberg principle, p² represents the frequency of the homozygous dominant genotype.

What does q² represent in the Hardy-Weinberg principle?

In the Hardy-Weinberg principle, q² represents the frequency of the homozygous recessive genotype.

What does pq represent in the Hardy-Weinberg principle?

In the Hardy-Weinberg principle, pq represents the frequency of the heterozygous genotype.