Selection & Speciation

Question 1

Causes of variation (sexual reproduction)

Answer 1

1. Mutation
2. Meiosis
3. Random fertilisation

Question 2

Mutation effects

Answer 2

• cause selective advantage
• be neutral
• cause selective disadvantage

Question 3

Environmental influences

Answer 3

Influences an organisms phenotype.
Affects way organisms genes are expressed
(Climatic conditions- temp, light intensity, humidity and abiotic/ biotic factors)

Question 4

Natural Selection Definiton

Answer 4

Process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population

Question 5

Natural Selection Process

Answer 5

Variation due to mutation;
Different selection pressures;
Selection for advantageous allele;
Selected organisms survive and reproduce;
Leads to change in allele frequency;
Occurs over a long period of time;

Question 6

Stabilising Selection

Answer 6

• Occurs in all populations where environment is stable.
• Selection pressure at both ends of distribution.
• Favours the average.
• Tends to eliminate extremes.
• Reduces variability
• Reduces opportunity for evolutionary change.

Question 7

Directional Selection

Answer 7

• Mean in population represents optimum phenotype for existing conditions
• Environmental change may produce new selection pressure that favours an extreme phenotype
• Changed conditions, favour allele combination necessary for survival
• Some organisms will possess the new optimum phenotype (allele combination)
• Over time, selection means this allele combination will predominate and the mean phenotype will shift.

Question 8

Disruptive Selection

Answer 8

• Is the opposite of stabilising selection
• Environment has selection pressures that favour 2 extreme phenotypes
• When conditions change the optimum phenotypes necessary for survival will also change
• Some organisms will possess the new extreme optimum phenotypes
• Over time selection means these 2 extremes will dominate and the mean will shift in both directions (towards extremes)
• It is the least common type of selection but it is the most important in evolution

Question 9

What is Speciation

Answer 9

• The evolution of a new species from existing species
• Species are groups of individuals with similar characteristics and same genes capable of interbreeding to produce fertile offspring.
• They belong to the same gene pool

Question 10

How do populations become distinct?

Answer 10

Two populations must undergo a period of reproductive isolation to become genetically distinct via a accumulation of mutations and different selection pressures

Question 11

Bottleneck definiton

Answer 11

random increase or decrease in allelic frequency. This is particularly important in small populations where the random loss of individuals with certain alleles results in a significant change in the frequency of alleles within the population and further generations

(Natural disaster)

Question 12

Founder effect definition

Answer 12

the change in allele frequency due to the migration of fertile individuals.

Question 13

Allopatric Speciation

Answer 13

selection occurs on either side of a geographical boundary that stops the organisms from interbreeding.

Question 14

Describe what is meant by speciation (allopatric)

Answer 14

• Geographical isolation;
• Separate gene pools
• Variation due to mutation;
• Different environmental conditions
• Selection for different characteristics
• Selected organisms survive and reproduce;
• Leads to change in allelic frequencies;
• Cannot breed to produce fertile offspring.

Question 15

Sympatric Speciation

Answer 15

‘same country’ and requires organisms in the same area to become reproductively separated for other reasons. This could be through choice of season to mate in

Question 16

Describe what is meant by speciation (sympatric)

Answer 16

• NOT Geographical isolation;
• Leads to reproductive isolation
• Separate gene pools
• Selection for different characteristics
• Selected organisms survive and reproduce;
• Leads to change in allelic frequencies;
• Cannot breed to produce fertile offspring

Question 17

Temporal Isolation

Answer 17

Organisms breed at different times of year

Question 18

Ecological Isolation

Answer 18

Different habitats within same area

Question 19

Behavioural Isolation

Answer 19

Different behaviour patterns e.g. courtship behaviour

Question 20

Mechanical Isolation

Answer 20

Anatomical differences making it impossible for gametes to come together

Question 21

Gametic Isolation

Answer 21

Incompatibility (genetic or physiological) between gametes prevent hybrid from forming

Question 22

Hybrid Isolation

Answer 22

Organisms interbreed but offspring are infertile:
E.g. horse and donkey can produce mule but mule is infertile

Question 23

Describe how bacteria can become resistant to antibiotics

Answer 23

• Variation
• Mutation
• Some plants have allele to survive;
• Adapted organisms reproduce;
• Increase in frequency of allele;
• No interbreeding

Question 24

Scientists’ analysis of blood proteins has indicated a lack of genetic diversity in populations of some organisms.

Describe the processes that lead to a reduction in the genetic diversity of populations of organisms.

Answer 24

1. reduced number of different alleles
2. Founder effect;
3. A few individuals from a population become isolated
4. (Genetic) bottlenecks;
5. (Significant) fall in size of population
6. Selective breeding
7. Using organisms with particular alleles