Question

Create the genetic basis of a dog (e.g. a locus with two or more alleles) for the phenotypic characteristic of the ear size

Then create a brief scenario of how the evolutionary forces Genetic Drift, Gene Flow/Migration,Natural Selection)
 might change the allele frequency and phenotype in the population

For example the trait is tentacle length in octopi and TT octopi have long tentacles, tt octopi have short tentacles and Tt octopi have intermediate tentacles.  In the habitat in which these octopi are found the ones with the longest tentacles on average get the most food.  You would continue to describe how the allele frequency and thus the average tentacle length would change.

Answer 1

The length of dog legs are controlled by a single gene locus. There are two alleles, which goven the length, dominant allele L which makes the dog taller and recessive allele l which makes them shorter. The alleles also exhibit codominance such that a dog with both L and l alleles will have front legs shorter than the back legs.
Dogs interbreed randomly in a population and as a result the gene pool is constantly shuffled and mixed. The dogs are under constant natural selection by their prey the rabbits. The rabbits run faster and to catch them dogs must also run faster. The dogs with longer legs can run faster and thus can outcompete the other dogs. Eventually the population will be dominated by the dogs with longer tails. The dogs with tall and short legs are also at advantage of not being able to run as fast as tall ones. however they do run faster than the shorter ones thus have higher genotype than the shorter ones.
The dogs were once seen as menace in society and government decided to kill them. The teams were sent to kill dogs, who would ley trap nd kill the dogs. The dogs fell to trap irrespective of their leg length and thus were randomly eliminated. This is a genetic drift.
Some dogs migrated to other localities in search of food and mate. The longer legged dogs made it to diverse areas and thus changed the genotypic frequency of the population. The increased inbreeding between long and short legged dogs due to migration and selection led to increase in frequency of codominant dogs.
Thus the cycle of gene frequency continued in a population.