natural selection

Question 1

what is evolution

Answer 1

the change in the frequency of alleles within a population over many generations

Question 2

why does variation happen

Answer 2

environmental factors
mutation: generation of new alleles
meiosis: independent segregation / crossing over
random fusion of gametes

Question 3

what happens in natural selection

Answer 3

1. there is variation in a population
2. because random mutations give rise to new alleles
3. organisms with advantageous alleles have a phenotype that gives them a selective advantage in their environment
4. so are more likely to survive to reproduce
5. passing on their advantageous alleles to the next generation
6. causing an increase in the frequency of the advantageous alleles in that population overtime

Question 4

what is directional selection

Answer 4

occurs when environment changes

acts against one extreme phenotype and selects the other

Question 5

what is stabilising selection

Answer 5

occurs in unchanging environment

acts against both extremes in a range of phenotypes, favouring middle

mode stays the same / range and standard deviation decrease

Question 6

what is disruptive selection

Answer 6

occurs in fluctuating environment

both extreme phenotypes have a selective advantage over the middle

intermediate phenotypes acted agains

Question 7

what is speciation

Answer 7

a process whereby one gene pool gives rise to more than one gene pool

Question 8

what is allopatric speciation

Answer 8

1. Parts of a population become geographically isolated
2. So no interbreeding occurs
3. Different environments lead to different selective pressures and different mutations lead to different advantageous alleles
4. In each population, organisms with advantageous alleles are more likely to survive and reproduce
5. Allele frequencies in populations change over generations
6. Eventually, genotypes become so different, that even if members of the different populations were reunited, they wouldn’t produce fertile offspring
7. The two populations are classified as different species

Question 9

what is sympatric speciation

Answer 9

sympatric speciation

Parts of a population become genetically / reproductively isolated:

• seasonal isolation → reproduce at different times of year ie. flowering plants
• mechanical isolation → anatomical difference prevent mating
• behavioural isolation → different courtship patterns
  1. So no interbreeding occurs
  2. Different environments lead to different selective pressures and different mutations lead to different advantageous alleles
  3. In each population, organisms with advantageous alleles are more likely to survive and reproduce
  4. Allele frequencies in populations change over generations
  5. Eventually, genotypes become so different, that even if members of the different populations were reunited, they wouldn’t produce fertile offspring
  6. The two populations are classified as different species

Question 10

what are selection pressures

Answer 10

selection pressures are environmental factors that affect chance of survival

• competition for food / mate
• temperature
• predation
• disease