Q) Explain how neutral mutations may be used as molecular clock to date evolutionary events

Since neutral mutations do not confer selective advantages or disadvantages to the individuals, it is assumed the rate of such mutations are fixed at a relatively constant rate. If the ancestral fossil of a particular species is available, the rate of mutation could be determined.

Hence, neutral mutations could be used as a molecular clock to date evolutionary events. For example, by comparing the DNA sequences of two related species of birds, the number of genetic differences between them could be used to calculate the length of time that has elapsed since divergence occurred.

Topic Evolution and Diversity: Q) Besides crossing over and independent assortment of pairs of homologous chromosome during meiosis, what are the other sources of genetic variation in a sexually reproducing population?

Ans: 
i) Gene and chromosomal mutation, 
ii) gene flow via migration of individuals into the population, 
iii) random mating between individuals within the population, and 
iv) random fusion of gametes during sexual fertilization.

Topic Evolution and Diversity Essay - Main Points!

Q)  How does classification and phylogeny differ from each other?

Main points
Key idea:	Principles of classification vs phylogeny
· Classification - group organisms based on their characteristics · Related organisms are first grouped as one species while related species are grouped into same genus · Ref to species + genus as lowest ranks in the classification sys and are used to name organism (i.e. binominal naming system) · Phylogeny - group organisms based on their evolutionary relationships which often involve comparison of DNA base sequences of genes inherited from ancestors to descendents · Ref to grouping organisms based on their characteristics derived from their recent ancestors
Key idea:	Hierarchical classification vs phylogenetic tree
· Classification - related genara are grouped into same family, related families grouped into same order, related orders grouped into same class, related classes grouped into same phylum, related phyla grouped into same kingdom, and related kingdoms into same domain · Ref to hierarchy of increasingly inclusive categories · Phylogeny - represented by a phylogenetic tree comprising of a series of two way branch points · Ref to each branch point as divergence of two evolutionary lineages from a common ancestor + tip of the branches are groups of organisms called taxa. Two related taxa will share a recent ancestral group represented by a branch point
Comments: (i) Visualize the answer through use of labelled diagram (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Use ‘comparative terms’ (e.g. unlike, whereas, etc) to answer this type of question (v) Note : for phylogenetic tree, it is common to use the term ‘clade’ in place of ‘taxon’. Clade is a special form of taxon and it should be monophyletic (i.e. comprises of ancestor and all its descendents)

Topic Evolution and Diversity Essay - Main Points!

Q) Suggest reasons for the polyphyletic evolution of viruses

Main points
Key idea:	Polyphyletic evolution + Reasons
· Results of sequencing of viral nucleic acids - viruses probably evolved from multiple origins (i.e. polyphyletic evolution) since their common ancestors cannot be determined easily · Reasons : (i) many diff types of viruses, (ii) all viruses are obligate parasites where they require a host cell for reproduction, so they evolve with their host cells including developing adaptive changes (e.g. to escape detection by immune cells)
Key idea:	Possible origin of viruses
·Through sequencing studies, viruses could originate as degenerate cell that lost their struc over time or were genes that ‘escaped’ from cells
Comments: (i) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (ii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iii) I have added an additional point to the worked solution (i.e. possible origin of viruses)

Topic Evolution and Diversity Essay - Main Points!

Q) Explain the benefits of the molecular classification of organisms

Main points
Key idea:	Basis of using molecular methods to classify organisms
· All organisms can be classified throu this method since all known life is based on nucleic acids · Involves comparing nucleotide bases b/w organisms to determine their evolutionary relatedness · Closely related organisms share similar base sequences as compared to distantly related organisms
Key idea:	Adv 1: Almost limitless set of characters for analysis
· Base sequences – each nucleotide base at each position of chrom can be considered as a character · Almost limitless no. of characters since genome of organisms consists of millions of nucleotides · Type of molecular data often used - DNA sequence of a gene that change (mutate) at a fairly constant rate + mutation that is selectively neutral
Key idea:	Adv 2: Molecular data is quantifiable and accessible
· Data can be submitted or retrieved from an online database to compute the probable relatedness of two organisms in a quantitative manner
Key idea:	Adv 3: Molecular data is objective (unambiguous)
· Avoids pitfalls of convergent evolution or subjective nature of distinguishing morphological struc
Key idea:	Adv 4: Differences in molecular data
· Differences in mol data can be used to (i) accurately determine degree of relatedness b/w organisms with very different phenotypes (ii) classify organisms even if their phenotypes are highly similar
Key idea:	Adv 5: Applicable even for extinct / non-living organisms
· Can classify organisms even if they are no longer living since DNA is highly stable so can be retrieved from living or dead cells · Once sequenced, data can be stored indefinitely (via electronic database)
Comments: (i) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (ii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iii) Assumption for Adv 5 - DNA is not degraded. Given the right conditions and the stability of DNA, this molecular method is especially useful for studying extinct species. (iv) I’ll modified the last point (Adv 4 & 5) slightly to make them easier to understand (hopefully !)