speciation

Question 1

suggest how speciation happens to produce 2 species of lemur on opposite sides of Madagascar

Answer 1

• geographical isolation (allopatric speciation)
• reproductive isolation/no gene flow/ separate gene pools
• different selection pressures/ different environmental conditions
• variation due to mutations in different populations
• advantageous allele passed on
• different species cannot breed to produce fertile offspring

Question 2

explain how evolutionary change over a long period of time has resulted in a great diversity of species

Answer 2

• evolution involves organisms adapting to their environment
• long period of time, many different environments result in many different adaptations
• therefore genetic diversity

Question 3

define sympatric speciation

Answer 3

individuals in same area are unable to reproduce due to differences in behaviour

Question 4

2 species of palm tree flower at different times. Suggest how these 2 species of palm tree arose by sympatric speciation
(5 marks)

Answer 4

• occurs in the same habitat/environment/population
• mutations cause different flowering times
• reproductive isolation/no gene flow/gene pools remain separate
• different alleles passed on
• change in frequency of alleles passed on
• disruptive selection
• eventually different species cannot interbreed to produce fertile offspring

Question 5

define genetic drift

Answer 5

change in allele frequency in a population between generations

Question 6

when there is continual substantial genetic drift what occurs

Answer 6

evolution

Question 7

explain why genetic drift is only important in small populations

Answer 7

each individual represents a large proportion of the population and there is a greater chance of allele being lost from the population

small populations have less variation and therefore less chance of adapting to challenging conditions

Question 8

Explain how new species are formed

Answer 8

New species are formed by speciation - the evolution of new species from existing ones

New species form when there is reproductive separation and then genetic change due to natural selection

Question 9

Explain how selection affects allelic frequencies

Answer 9

Allelic frequency is the number of times an allele occurs within the gene pool.

This is affected by selection which in turn is affected by environmental conditions

Question 10

What are populations showing little genetic variation more susceptible to?

Answer 10

new disease and climate change

Question 11

Which form of selection is this?

preserves the characteristics of a population

Answer 11

stabilising selection