Evolution may lead to speciation

Question 1

Why may phenotype vary within a species?

Answer 1

Due to genetic + environmental factors

Question 2

What are the genetic factors that cause phenotypic variation within a species?

Answer 2

1- Mutation of alleles
2- Random fertilisation by gametes
3- Random assortment of genetic material during meiosis

Question 3

Why does natural selection occur?

Answer 3

1- Predation
2- Disease
3- Competition
All result in different survival + reproduction

Question 4

How does natural selection cause a change in a population’s gene pool over generations?

Answer 4

Organisms with the advantageous characteristics are more likely to survive + reproduce so pass favourable alleles to offspring. This changes the allele frequencies within a gene pool

Question 5

Stabilising selection

Answer 5

• Occurs when environmental conditions stay the same
• Individuals closest to the mean are favoured, any new characteristics are selected against
• Results in low diversity

Question 6

Directional selection

Answer 6

• Occurs when environmental conditions change
• Individuals with phenotypes suited to new conditions will survive + pass on their genes
• Over time the mean of the population will move towards these. characteristics

Question 7

Disruptive selection

Answer 7

• Individuals which contain alleles which code for either extreme trait are more likely to. survive + pass on alleles
• Both extremes are favoured over the mean
• Allele frequency changes + more individuals possess allele for extreme trait + middling trait becomes less frequent
• Can lead to speciation

Question 8

Speciation

Answer 8

The process that results in the creation of new species
- Occurs when one original population of the same species becomes reproductively isolated
- This means there’s now 2 populations of the same species but they can’t breed together
- This can result in the accumulation of differences in their gene pools to the extent that the 2 populations would be unable to interbreed to make fertile offspring + are classed as different species

Question 9

Allopatric speciation

Answer 9

Populations can become separated geographically leading to reproductive isolation
- Separation results from a physical barrier e.g. river, mountain range
- This separates the original population into 2 which are now unable to reproduce due to geographical barrier
- Both separate populations will continue to accumulate different beneficial mutations over time to help them survive + over many generations their DNA becomes so genetically different they are unable to interbreed to create fertile offspring, so are classed as 2 different species

Question 10

Sympatric speciation

Answer 10

Populations can become reproductively isolated due to differences in their behaviour
- Still unable to reproduce + this could be because of a random mutation that could impact reproductive behaviour e.g. it may cause individuals to perform a different courtship ritual or for individuals to become fertile at different times of year
- Due to this, individuals will not reproduce together + there will be no gene flow between the 2 groups
- Overtime these reproductively isolated populations will accumulate different mutations to the extent their DNA is different so they can’t interbreed to produce fertile offspring so are classed as 2 different species

Question 11

Genetic drift

Answer 11

Change in the allele frequency within a population between generations
- Will always be a genetic drift from one generation to the next but continual, substantial genetic drift results in evolution
- The smaller a population, the bigger the impact allele frequency changes have proportionally + this is why evolution occurs more rapidly in smaller populations

Question 12

Evolution

Answer 12

Change in allele frequencies in a population