Describe how natural selection leads to evolution.

Explain the consequences of altering a DNA base in the genome of an organism.

populations produce more offspring than can survive;
individuals show variation;
limited resources;
create a struggle for survival/competition;
survival of the fittest / some are better suited to the environment and survive;
variation/characteristic must be heritable;
best fitted individuals survive to reproduce;
advantageous variation/characteristic/allele passed on;
over time advantageous variation/characteristic/allele increases in the population;

altering a base (in DNA) is a (point) mutation;
only has an effect if base is in a gene;
when mRNA is produced by transcription one mRNA base is different;
one codon in mRNA is different;
one amino acid is different in the polypeptide;
polypeptide produced by translation of mRNA;
some base changes do not change the amino acid coded for;
structure of polypeptide /protein may be altered;
usually the polypeptide/protein does not function as well;

example given:
disease: sickle cell anemia;
mutation: GAG to GTG;
consequence in translation: glutamic acid to valine;
consequence for protein: hemoglobin altered so sickle cell formed;
consequence for individual: less oxygen can be carried;

The role of natural selection in evolution was not well answered even though it is a fundamental concept in biology.  The best answered laid out a step-wise sequence of events that lead to evolution with real life examples to illustrate the explanation such as Galapagos Island Finches.

The consequences of altering a base in the genome of an organism should be a straightforward question to answer but many candidates rambled without giving specifics. The best answers laid out a step-wise sequence of events that explain the consequences with real life examples to illustrate the explanation such as Sickle cell anaemia.