3.3.8 Evolution may lead to Speciation Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

What is evolution?

A

Is the change in allele frequencies in a population over time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Name 2 methods in which evolution occurs

A
  1. Natural selection
  2. Genetic drift
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe how natural selection occurs by evolution

A
  1. Selection pressures (e.g. predation, disease, competition) create struggle for survival
  2. Genetic variation between individuals
  3. Individuals with (beneficial) allele that makes them better adapted to selection pressure than others
  4. This increases their chance of survival & more likely to reproduce and pass on this (beneficial) allele
  5. Increased freqency of beneficial alleles in next generation
  6. Offspring more likely to survive, reproduce and pass on their alleles
  7. ∴ frequency of beneficial alleles in gene pool increases from generation to generation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Name 4 observations Darwin made

A
  • Population remain stable
  • Offspring appear similar to their parents
  • No two individuals are the same
  • Organisms have the ability to reproduce
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What type of variation results in evolution?

A

Only genetic variation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a selection pressure?

A

Anything that affects an organism’s chance of survival and reproduction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Name 3 selection pressures

A
  • Human activity / pollution
  • Availability food sources
  • Diseases
  • Competition
  • Predators
  • Land clearance
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Types of natural selection affect ____ ______ in different ways

A

allele frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Name the 3 types of natural selection

A
  • Stablising Selection
  • Directional Selection
  • Disruptive Selection
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Define Stablising Selection

A

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce

(Favours the average = averages increase and extremes decrease)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When does stablising selection occur?

A

Occurs when environment isn’t changing = reduces range of possible phenotypes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Define Directional Selection

A

Where individuals with alleles for single extreme phenotype are more likely to survive and reproduce

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When does directional selection occur?

A

Occurs in response to environmental change

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe Disruptive Selection

A

Where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

When does speciation occur?

A

When populations of same species become reproductively isolated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Name the 2 types of speciation

A
  • Allopatric Speciation
  • Sympatric Speciation
17
Q

What does allopatric speciation involve?

A

Geographical isolation

18
Q

Describe allopatric speciation (6x)

A
  1. Populations that are geographically separated will experience slightly environmental different conditions
  2. Populations will experience different selection pressures ∴ = selection for different alleles
    1. Variation due to mutation
  3. Selection for advantageous allele = selected organisms survive and reproduce
  4. Leads to changes in allele frequency
  5. Eventually, individuals from different populations changed so much = can’t breed to produce fertile offspring
    • Become reproductively isolated
  6. 2 groups = become separate species
19
Q

Allopatric Speciation

Name 3 ways in which different changes in allele frequencies could occur

A
  • Different alleles could be more favourable in new conditions and directional selection could take place
    • e.g. colder climate: directional selection will act on alleles for fur length = increasing frequency of allele for longer fur length
  • Mutations could occur in each population
  • Genetic drift
20
Q

What is sympatric speciation caused by?

A

Mutations, changes in mating patterns

21
Q

Describe how sympatric speciation could occur due to mutations

A
  1. Most eukaryotic organisms = diploid
    1. Sometimes mutations occur that increase no. of chromosomes
    2. Known as polyploidy
  2. Individuals with different no. of chromosomes can’t reproduce sexually to give fertile offspring
    • e.g. polyploid organism in diploid population = reproductively isolated
  3. If polyploid organism reproduces asexually = new species develops
22
Q

Sympatric speciation is more common in ____ than ______

A

plants than animals

23
Q

Why does reproductive isolation occur?

A

Occurs ∵ changes in alleles and phenotypes in some individuals prevent breeding successfully with individuals without these changes

24
Q

Name 3 examples of changes that occur to individuals that leads to reproductive isolation

A
  • Seasonal
    • Different flowering or mating seasons
    • Or become sexually active at different times of year
  • Mechanical
    • Changes in genitalia prevent successful mating
  • Behavioural
    • Develop courtship rituals that aren’t attractive to main populations
25
Q

What is genetic drift?

A

When chance rather than environmental factors dictates which individuals survive, breed and pass on their alleles

26
Q

Give an example of how genetic drift could lead to speciation

A
  1. Individuals within population show variation in their genotypes
  2. By chance, allele for one genotypes (B) is passed on to offspring more often than others
  3. ∴ no. of individuals with the allele increases
  4. Changes in allele frequency in 2 isolated populations could eventually lead to reproductive isolation and speciation
27
Q

Evolution by genetic drift has greater effect in ____ populations

A

smaller

28
Q

Why does genetic drift have a greater effect in smaller populations?

A

∵ chance has greater influence in smaller populations

(In larger populations, any chance variations in allele frequency tend to even out across whole population)

29
Q

Explain how an insect population can become resistant to an insectidice (3)

A
  • mutations
  • producing alleles giving resistance
  • natural selection / leads to increased frequency of alleles in population
30
Q

Copper-tolerant grass produces its flowers eariler in the year than non-tolerant grass of the same species. Explain how this might produce two different species of grass. (5)

A
  1. (populations are) reproductively isolated (due to different flowering times)
  2. ∴ no flow of alleles between the populations/different (random) mutations in each group
  3. different selection pressures
  4. frequency of alleles will change
  5. (genetic differences lead to) members of populations become unable to interbreed and produce fertile offspring
31
Q

One farmer stated that the increase in the use of Bt crop plants had caused a mutation in one of the insect species and that this mutation had spread to other species of insect. Was he correct? Explain your answer. (4)

A
  • Mutations are random
  • Only the rate of mutation is affected by environment
  • Different species do not interbreed / do not produce fertile offspring
  • So mutation/allele cannot be passed from one species to another
32
Q

There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin. Explain why there was a time lag. (3)

A
  1. Initially one insect with favourable mutation / allele;
  2. Individuals with (favourable) mutation / allele will have more offspring
  3. Takes many generations for (favourable) mutation / allele to become the most common allele