1Explain how sympatric speciation of guinea pigs might occur (3 marks)
Random genetic mutation
Causes different breeding season/courtship behaviour
Different selection pressures/changes in allele frequency
2What is allopatric speciation? (2 marks)
New species from different populations
In different areas / from isolated populations
3What is sympatric speciation? (2 marks)
Formation of new species
From a population living in the same area
4Explain how different species evolve when a species is separated into small lakes and streams (5 marks)
Geographical isolation
Variation due to mutation
Differnt evironmental conditions / selection pressures
Selection for different advantageous alleles
Causes change in allele frequency
5WrWr = resistant
WrWs = resistant
WsWs = not resistant
51% rats = resistant
Use HW equation to estimate % of rats heterozygous for resistance (3 marks)
p$2$ + 2pq = 0.51
q$2$ = 0.49
q = 0.7
p = 0.3
p$2$ = 0.09
0.51 - 0.09 = 0.42 x 100 = 42%
6Give 5 assumptions made when using the HW equation (5 possible marks)
No migration
No selective advantage
Large population
Random mating
No mutation
7Explain how resistance to an antibiotic could become widespread in a bacterial population following a gene mutation in just one bacterium (5 marks)
Frequent antibiotic use creates selection pressure / kills bacteria
Bacteria with resistance have advantage over others
Reproduce more than other types so pass on advantageous allele
AA frequency increases in subsequent generations
Resistant frequency increases in subsequent generations
8Explain what is meant by stabilising selection and describe the circumstances under which it takes place (4 marks)
Occurs in an unchanging environment
Selection against extremes
Range/SD reduced
Increasing proportion of populations becomes well adapted to environment
92 species of tree arise via sympatric speciation
Flowering times of the 2 species are different
Suggest how these 2 species arose (6 marks)
Occurs in same habitat/environment
Mutations cause different flowering times
Reproductive isolation
Change in allele frequency
Disruptive selection
Eventually different species cannot interbreed to produce fertile offspring