3.7.3 - Evolution May Lead to Speciation

Question 1

variation due to genetic factors

Answer 1

• mutation
• meiosis
• random fertilisation of gametes

Question 2

variation due to environmental factors

Answer 2

• climatic conditions (e.g. temperature, rainfall, sunlight)
• soil conditions
• pH
• food availability

Question 3

selection pressures

Answer 3

• predation
• disease
• competition

Question 4

stabilising selection

Answer 4

• preserves the average phenotype of a population by favouring average individuals
• selection against the extreme phenotypes
• e.g. human birth weights

Question 5

directional selection

Answer 5

• selection for one extreme phenotype
• e.g. antibiotic resistance in bacteria

Question 6

disruptive selection

Answer 6

• opposite of stabilising selection
• favours extreme phenotypes

Question 7

allopatric speciation

Answer 7

• geographical isolation
• reproductive isolation (no gene flow)
• different selection pressures
• mutations in different populations
• advantageous alleles passed on/selected for → change in allele frequency
• eventually different species cannot interbreed to produce fertile offspring

Question 8

causes of genetic variation

Answer 8

• mutation
• crossing over
• independent segregation (of homologous chromosomes)
• random fertilisation of gametes