Selection & Speciation

Question 1

Name the main causes for genetic variation

Answer 1

• mutation
• meiosis
• random fertilisation
• random fusion of gametes

Question 2

Define Natural Selection

Answer 2

process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of frequency of the advantageous allele within the population

Question 3

What is Natural Selection

Answer 3

• variation within population
• better adapted individuals more likely to survive and reproduce
• these organisms are more likely to pass on their alleles
• those which are less well adapted fail to survive and reproduce
• organisms therefore subject to different selection pressures due to different environment which determines spread of alleles within gene pool.
• selection pressures can be either abiotic & biotic

Question 4

What is stabilising selection

Answer 4

• environment is stable and there are selection pressures at both ends of distribution
• favours average and tends to eliminate extremes
• reduces variability and reduces opportunity for evolutionary change

Question 5

What is directional selection

Answer 5

• favours average and environmental changes may produce selection pressures which favours the optimum phenotype
• over time selection means allele combination will predominate and mean phenotype will shift

Question 6

What is disruptive selection

Answer 6

• environment has selection pressures which favour 2 optimum phenotypes
• over time selection means these 2 extremes will dominate and the mean will shift in both directions

Question 7

What is speciation

Answer 7

• evolution of new species from existing species
• if two populations can interbreed, they will not evolve into two distinct species
• two populations must undergo a period of reproductive isolation to become genetically distinct via a accumulation of mutations and different selection pressures

Question 8

What is allopatric speciation

Answer 8

• geographical isolation
• no interbreeding between populations
• variation due to mutation
• different selection pressures
• selection for advantageous allele
• differential reproductive success
• increase in frequency of alleles
• no interbreeding

Question 9

what is sympatric speciation

Answer 9

• not geographical isolation
• leads to reproductive isolation
• no interbreeding between populations
• selection for advantageous allele
• differential reproductive success
• leads to a change in allelic frequency
• no interbreeding