Chapter 7: Diversity and Evolution

Chapter 7: Diversity and Evolution
This is personally one of my favourite topics because of how much misconceptions common folk have about evolution and it is always fun to hear them speak confidently of those misconceptions.
I have a blog post dated 26/03/16 where I describe my journey to National University of Singapore Lee Kong Chian Natural History Museum for an evolution workshop.

Syllabus Objectives:
1. Explain binomial nomenclature of a species and hierarchical classification.
2. Describe classification of species into taxonomic groups and explain various concepts of species.
3. Explain how species are formed with reference to geographical isolation, physiological isolation and behavioural isolation.
4. Explain the relationship between classification and phylogeny.
5. Explain why variation is important in selection.
6. Explain, with examples, how environmental factors act as forces of natural selection.
7. Explain how natural selection may bring about evolution.
8. Explain why the population is the smallest unit that can evolve.
9. Explain how homology (anatomical, embryological and molecular) supports Darwin's theory of natural selection (emphasis on descent with modification).
10. Explain how biogeography and fossil records support evolutionary deductions based on homologies.
11. Explain importance of use of genome sequences in reconstructing phylogenetic relationships and state advantages of molecular (nucleotide and amino acid sequences) methods in classifying organisms.
12. Explain how genetic variation (including recessive alleles) may be preserved in a natural population.
13. Briefly describe the neutral theory of molecular evolution in terms of mutations producing new molecular variants which are selectively neutral. (Knowledge of genetic drift and molecular clock required)

Content:
1. Explain binomial nomenclature of a species and hierarchical classification.
Binomial nomenclature is a system of giving a scientific name, consisting of a genus name and species name.
Note: In writing, scientific names require underlining.
Taxonomy is the science of classifying organisms based on shared features into:
Kingdom, Phylum, Class, Order, Family, Genus and Species.

2. Describe classification of species into taxonomic groups and explain various concepts of species.
Down the taxonomic ranks, number of species decreases, number of shared features increases, among species.
Conditions for one species:

1. Biological Species Concept (BSC): Able to interbreed to produce viable, fertile offspring.
2. Morphological Species Concept (MSC): Similarities in measurable anatomical and physical features.
3. Ecological Species Concept (ESC): Adapted to the same ecological niche. (Sum use of resources)
4. Phylogenetic Species Concept (PSC): Smallest group that shares a common ancestor.

3. Explain how species are formed with reference to geographical isolation, physiological isolation and behavioural isolation.

• Speciation is the divergence of one species from another, caused by reproductive barriers, both prezygotic and postzygotic, that results from changes in allelic frequencies, based on BSC.
• Geographical isolation is a prezygotic barrier that results in allopatric speciation due to different selection pressures, and new alleles arise from mutation independently in separated populations, causing genetic divergence.
• Physiological isolation is a prezygotic barrier due to mechanical isolation where male and female sex organs are structurally incompatible, or gametic isolation where male and female gametes are unable to fuse/ survive due to incompatibility.
• Behavioural isolation is a prezygotic barrier due to difference in mating rituals, recognised only by same species.

4. Explain the relationship between classification (taxonomy) and phylogeny.
Differences in terms of:

1. Classification basis: (T)Shared features (P)Homology
2. Method: (T)Observation of physical characteristics (P)Homology: Molecular evidence, fossil records, physical characteristics
3. Ranking of groups:(T) K, P, C, O, F, G, S (P)none
4. Reflection of evolutionary history: (T)may not reflect (P)reflects
5. Purpose: (T)Group based on similarities (P)Reflection ancestor-descendant relationships

5. Explain why variation is important in selection.

Variation caused by gene mutation/ chromosomal aberration gives rise to new alleles, increasing gene pool of a population.

Variation caused by sexual reproduction gives rise to new combinations of alleles, due to crossing-over of homologs, independent assortment, random segregation and random fertilisation.

During natural selection, variation allows selection pressures to select for advantageous traits for higher survival rates and reproductive success, to pass down favourable alleles to offspring.

6. Explain, with examples, how environmental factors act as forces of natural selection.

Industrial Melanism (Selection pressure: Predators):

Before, light-coloured moths had selective advantage as it was well camouflaged with light-coloured environment, increasing allelic frequency of light-coloured moths.

After, light-coloured moths had selective disadvantage as it was unable to camouflage with the now-dark-coloured environment, decreasing allelic frequency of light-coloured moths.

Antibiotic Resistance (Selection pressure: Antibiotics):

Before, non-resistant strains were killed, resistant strains had selective advantage, decreasing allelic frequency of non-resistant strains.
After, resistant strains survive and pass on favourable antibiotic resistant genes to offspring by binary fission, increasing allelic frequency of resistant strains.

7. Explain how natural selection may bring about evolution.