Evolution and Speciation

Question 1

What causes phenotypic variation?

Answer 1

• Genetic variation
• Environment

Question 2

What is the primary cause of genetic variation?

Answer 2

Mutation

Question 3

How do mutations cause genetic variation?

Answer 3

Mutation results in the generation of new alleles.
- The new allele may be advantageous, disadvantageous or have no apparent effect on phenotype
- New alleles are not always seen in the individual that they first occur in
- They can remain hidden within a population for several generations before they contribute to phenotypic variation

Question 4

What are other causes of genetic variation?

Answer 4

1. Crossing over of non-sister chromatids during prophase I of meiosis
2. Independent assortment of homologous chromosomes during metaphase I of meiosis
3. Random fusion of gametes during fertilisation

Question 5

How does crossing over cause genetic variation?

Answer 5

It can result in a new combination of alleles on the two chromosomes. (Genetic variation between gametes produced by an individual)

Question 6

How does independent assortment cause genetic variation?

Answer 6

Causes different combinations of chromosomes in daughter cells. (Genetic variation between gametes produced by an individual)

Question 7

How does random fertilisation cause genetic variation?

Answer 7

Each gamete carries substantially different alleles. (Genetic variation between zygotes and resulting individuals)

Question 8

What is natural selection?

Answer 8

The process by which individuals with a fitter phenotype are more likely to survive and pass on their alleles to their offspring so that the advantageous alleles increase in frequency over time and generations.

Question 9

What is genetic drift?

Answer 9

A gradual change in allele frequencies in a small population due to chance and not natural selection.

Question 10

What does selective advantage result in?

Answer 10

1. Individuals with phenotypes providing selective advantages are likely to produce more offspring and pass on their favourable alleles to the next generation
2. Over time, this differential reproductive success has an effect on the allele frequencies within a gene pool
3. Alleles that are favourable will increase in frequency in a gene pool
4. Alleles that are not favourable will decrease in frequency in a gene pool

Question 11

What are the types of selection?

Answer 11

• directional
• stabilising
• disruptive

Question 12

Describe disruptive selection.

Answer 12

Natural selection that maintains high frequencies of two different sets of alleles.

Question 13

What is evolution?

Answer 13

The formation of new species from pre-existing species over time, as a result of changes to gene pools and allele frequencies from generation to generation.

Question 14

What changes can lead to reproductive separation?

Answer 14

Seasonal changes - some individuals in a population may develop different mating or flowering seasons to the rest of the population
Mechanical changes - some individuals in a population may develop changes in their genitalia that prevent them from mating successfully with individuals of the opposite sex
Behavioural changes - some individuals in a population may develop changes in their courtship behaviours, meaning they can no longer attract individuals of the opposite sex for mating

Question 15

What are the types of speciation?

Answer 15

• Allopatric
• Sympatric

Question 16

Describe allopatric speciation.

Answer 16

• Allopatric speciation occurs as a result of geographical isolation due to geographical barriers. These may be natural (e.g. lake or mountain range), or man-made (e.g. motorway)
• This creates two populations of the same species who are reproductively separated from each other, and as a result, no genetic exchange can occur between them
• If there are sufficient selection pressures acting to change the gene pools within both populations then eventually these populations will diverge and form separate species
• The changes in the alleles/genes of each population will affect the phenotypes present in both populations
• Over time, the two populations may begin to differ physiologically, behaviourally and morphologically

Question 17

Describe sympatric speciation.

Answer 17

• Sympatric speciation takes place with no geographical barrier
• A group of the same species could be living in the same place but in order for speciation to take place there must exist two populations within that group and no gene flow occurs between them
• Therefore, something has to happen that splits or separates the two populations:
• Ecological separation: Populations are separated because they live in different environments within the same area
• Behavioural separation: Populations are separated because they have different behaviours

Question 18

Explain how speciation can occur due to geographical barriers?

Answer 18

1) Geographic isolation / allopatric
2) Reproductive separation
3) Different selection pressures
4) Random advantageous mutation
5) Alleles are passed on over many generations
6) Allele frequency increases
7) Eventually, the 2 populations can no longer interbreed

Question 19

features of licen/ saprobionts

Answer 19

• 2 different species co existing
• made up of algae: : can photosynthesise so creating glucose, carbohydrates which it shares w fungus
• made up of fungus: can absorb water and release extracellular enzymes onto rock which can break down rock to release minerals
• meaning theyre able to survive even though:
• little water available
• no food source
• no minerals