7.3 Evolution may lead to speciation

Question 1

Explain why individuals within a population of a species may show a wide range of variation in phenotype

Answer 1

● Genetic factors
○ Mutations = primary source of genetic variation
○ Crossing over between homologous chromosomes during meiosis
○ Independent segregation of homologous chromosomes during meiosis
○ Random fertilisation of gametes during sexual reproduction

● Environmental factors (depends on context - eg. food availability, light intensity)

Question 2

What is evolution?

Answer 2

● Change in allele frequency over time / many generations in a population

● Occurring through the process of natural selection

Question 3

Describe factors that may drive natural selection

Answer 3

● Predation, disease and competition for the means of survival

● These result in differential survival and reproduction, ie. natural selection

Question 4

Explain the principles of natural selection in the evolution of populations

Answer 4

1. Mutations - Random gene mutations can result in [named] new alleles of a gene
2. Advantage - Due to [named] selection pressure, the new allele might benefit its possessor [explain why] → organism has a selective advantage
3. Reproduction - Possessors are more likely to survive and have increased reproductive success
4. Inheritance - Advantageous allele is inherited by members of the next generation (offspring)
5. Allele frequency - Over many generations, [named] allele increases in frequency in the gene pool

Question 5

Explain the effects of stabilising selection

Answer 5

● Organisms with alleles coding for average / modal variations of a trait have a selective advantage (eg. babies with an average weight)

● So frequency of alleles coding for average variations of a trait increase and those coding for extreme variations of a trait decrease

● So range / standard deviation is reduced