Evolution

Question 1

What is evolution?

Answer 1

Evolution is the change overtime in the proportion of individuals in a population differing in one or more inherited traits.

Question 2

What is the main source of genetic variation within a population?

Answer 2

random mutation

Question 3

By what processes can evolution occur through?

Answer 3

Evolution can occur through the random process of genetic drift or the non-random processes of natural selection and sexual selection.

Question 4

What is natural selection?

Answer 4

Natural selection is a non-random increase in allele frequency that favours survivals.

Question 5

Describe the process of natural selection.

Answer 5

As organisms produce more offspring than the environment can support, those individuals with variations that best fit their environment are the ones most likely to survive and breed. Through inheritance, these favoured traits are therefore likely to become more frequent in subsequent generations.

Question 6

What is sexual selection?

Answer 6

non-random increase in the frequency of alleles that make mating and reproduction more likely.

Question 7

What does sexual selection result in?

Answer 7

This results in characteristics which increases the chance of mating may become exaggerated but may also decrease the organism’s chances of survival.

Question 8

What is genetic drift?

Answer 8

Genetic drift refers to a change in the frequency of alleles in a population as a result of a random event.

Question 9

What does genetic drift have more significant impact on and why?

Answer 9

Genetic drift has a more significant impact in small populations because alleles are more likely to be lost from the gene pool.

Question 10

Describe the bottleneck effect.

Answer 10

Natural disasters can reduce the size of the population significantly. Other examples include hunting or habitat destruction.
Surviving smaller populations most likely won’t represent the original population’s gene pool.
 Some alleles may be over-represented.
 Some alleles may be under-represented.
 Some alleles may have been lost.

Question 11

What can genetic drift lead to?

Answer 11

Genetic drift leads to the loss of rare alleles and a decrease in the gene pool.

Question 12

What can genetic drift cause?

Answer 12

It can cause a new population to be genetically distinct from its original population.
This has led to the hypothesis that genetic drift plays a role in the evolution of a new species.

Question 13

What is gene flow?

Answer 13

Gain or loss of alleles from a population by the movement of individuals or gametes into or out of the population.

Question 14

Describe the effect of gene flow.

Answer 14

Gene flow reduces the differences between populations are sharing alleles.
If widespread enough then 2 separate populations could become 1 with one common gene pool.

Question 15

What do disadvantageous mutations do?

Answer 15

Disadvantageous mutations reduce the individual’s evolutionary fitness

Question 16

What effect do neutral mutations have on evolutionary fitness?

Answer 16

no effect

Question 17

In rare case what can mutations be?

Answer 17

In rare cases they may be beneficial (advantageous) to the fitness of an individual.

Question 18

What can mutations which were once neutral or disadvantageous become?

Answer 18

A mutation that was once neutral or disadvantageous can become advantageous in altered environments. This can be as a result of natural selection and lead to speciation.

Question 19

What is genetic fitness?

Answer 19

The reproductive success of a genotype, usually measured as the number of offspring produced by an individual that survive to reproductive age relative to the average for the population.

Question 20

What is absolute fitness? (Describe in detail)

Answer 20

Absolute fitness is the ratio of frequencies of a particular genotype from one generation to the next.
That is the ratio between the number of individuals with a particular genotype after selection, compared to the number with that same particular genotype before selection.
If the absolute fitness is 1, then the frequency of that genotype is stable. A value greater than 1 conveys an increase in the genotype and, therefore, a value less than 1 conveys a decrease.

Question 21

What is relative fitness?

Answer 21

Relative fitness is the ratio of surviving offspring of one genotype compared with other genotypes.

Question 22

Where selection pressures are high what can the rate of evolution be?

Answer 22

Where selection pressures are high, the rate of evolution be rapid.

Question 23

What 4 factors increase the rate of evolution?

Answer 23

• Shorter generation times
• Warmer environments
• Vertical gene transfer (sexual reproduction)
• Horizontal gene transfer

Question 24

What do selection pressures affect?

Answer 24

Selection pressures affect the heritability of certain traits

Question 25

In natural selection, what do selection pressures affect?

Answer 25

In natural selection, selection pressures affect the individual’s chances for survival.

Question 26

In sexual selection, what do selection pressures affect?

Answer 26

In sexual selection, selection pressures affect the individual’s reproductive success.

Question 27

Describe how shorter generation times can increase the rate of evolution.

Answer 27

In short generation times, there are more generations in a shorter period of time. Since evolution happens over generations, having more generations provides more opportunities for selection pressures to have an effect on a population. This means that organisms that have shorter generation times are likely to evolve at a faster rate.

Question 28

Describe how warmer environments can increase the rate of evolution.

Answer 28

Most organisms do not regulate their body temperature, which remains the same as their environment. When the environment gets warmer, all the enzymes in the organism work faster. The germ cells which produce gametes divide more frequently, resulting in more DNA replication and therefore increasing the chance of mutations, i.e. increasing rate of evolution.

Question 29

Describe how sexual production can increase the rate of evolution.

Answer 29

Combining genetic material from two different individuals during sexual reproduction increases variation. Greater variation leads to more selection and a faster rate of evolution. It also results in beneficial DNA sequences becoming shared, producing offspring with new combinations of beneficial alleles.

Question 30

Describe how horizontal gene transfer can increase the rate of evolution.

Answer 30

Many prokaryotes, such as bacteria, that reproduce principally by asexual reproduction have mechanisms for horizontal gene transfer between individuals they can pass DNA back and forth to one another directly. By packing bacterial genes into plasmids and ‘injecting’ them into other bacteria. This means that bacteria do not have to rely on random mutations to produce a beneficial gene variant. One species might ‘pick up’ an advantageous gene from another species horizontally. The process of natural selection could begin right away, spreading the new variant through future generations.

Question 31

Describe how horizontal gene transfer can speed up the evolution of antibiotic resistance.

Answer 31

No need to wait for useful mutation. Another strain may have already encountered penicillin and already acquired a useful mutation i.e. resistance to penicillin. This means that a population that encounters penicillin for the first time may already include some individuals that carry resistance genes. This allows the strain to evolve quickly to evade the antibiotic.

Question 32

What is co-evolution frequently seen in?

Answer 32

Co-evolution is frequently seen in pairs of species that demonstrate a symbiotic relationship

Question 33

Give 5 examples of co-evolution.

Answer 33

 Herbivores and plants  Pollinators and plants  Predators and their prey  Parasites and their hosts

Question 34

Describe co-evolution between herbivores and plants.

Answer 34

Plants have evolved both chemical and structural defences in response to grazing, including the production of deadly internal chemicals and toxins or external thorns and stings. Over many generations, grazers have subsequently undergone random mutations that have been favoured by natural selection, evolving to overcome some of these defences and so the race continues.

Question 35

Give an example of co-volution between herbivores and plants?

Answer 35

An example of co-evolution is the old world swallowtail caterpillar, living and feeding on the fringed rue plant. The rue produces toxic oils which deter plant-eating insects. The old world swallowtail caterpillar has evolved tolerance to these toxins, which allows it to continue to feed on the rue and has the added benefit of reducing competition with other plant-eating insects.

Question 36

Describe co-evolution between plants and their pollinators. (use example to help)

Answer 36

The symbiosis between plants and their pollinators is an example of mutualism, whereby both species benefit. The white orchid, and African moths have co-evolved, with the moths receiving nutritious nectar and the flowers relying on the moths to spread pollen so they can reproduce. Flowers that are pollinated by birds produce nectar, which provides energy for the birds. To attract the birds, these flowers have undergone random mutations, favoured by natural selection to evolve their colour and shape to be best suited to attracting the pollinator in question.

Question 37

Describe co-evolution between predators and their prey.

Answer 37

Predator-prey relationships are those involving predation, in which a predator eats its prey. Successful predators may have evolved adaptations, such as acute senses, claws, teeth, fangs, stingers or poison, that can help them to catch and feed on prey. Prey species have also evolved adaptations, from passive defences, such as hiding and camouflage, to active defenses, such as escaping or defending themselves.

Question 38

Describe co-evolution between parasites and their hosts. Give example.

Answer 38

Parasitism involves a relationship whereby a parasite lives on a host, gaining resources and a place to live. This is of benefit to the parasite, while the host is harmed. E.g. malaria, plasmodium falciparum and humans.

Question 39

In co-evolution, what does a change in the traits of one species acts as?

Answer 39

a selection pressure on the other species.

Question 40

Explain the red queen hypothesis.

Answer 40

The co-evolutionary ‘arms race’ between a parasite and its host is known as the Red Queen hypothesis because both organisms must ‘keep running in order to stay still’. Co-evolution is where evolution merely permits organisms to maintain their current success.