llustrate the role of each area in the evolution of the Hebe
Uses appropriate examples from the Hebe data to illustrate the role of each area/concept in the evolution of the Hebe. In doing so, explains the biology involved. Note: a definitive example is not expected; rather the candidate needs to choose likely and appropriate examples to illustrate each area.
Explains the process of natural selection resulting in the adaptations of the whipcord species to the alpine environment or the larger leaved species to the lower light but higher water level environments of other environments. (OR any other appropriate selection pressure.)
- Mutations: Aneuploidy OR Polyploidy
Aneuploidy
Links the process of aneuploidy to an example such as the ancestral form which likely had n = 21 therefore any Hebe with n = 20 could be an aneuploid due to the loss of one chromosome;
Polyploidy
Links the process of polyploidy to an example. There are several examples where there is a doubling or tripling of the chromosomal number eg H. gracillima (n = 40) and H. venustula (n = 60).
- Genetic Drift OR Founder Effect
Founder effect
The Founder effect is where a small population has become isolated and does not represent the main population in its genetic constitution. The NZ Hebe are a small and genetically unrepresentative population compared with the original Australian population because of the likely single introduction.
OR The Founder effect could also occur where a small group of Hebe became isolated from the main population and did not represent the main population in its genetic constitution. This could have happened during both the mountain uplift and glaciation periods when populations became isolated, eg H. hectorii, which is found on the wet side of the South Island, while most of the other whipcords are found on the dry side.
Genetic drift
Change in allele frequency (loss of allele from population / fixation of an allele) due to chance events in a small isolated population.