The five answers listed are all assumptions of Hardy-Weinberg equilibrium except for the population being small. In fact, the population must be large so that random chance during mating and death will not result in certain alleles changing their proportion in the population.

In order to answer this question, you must remember the Hardy-Weinberg equations. 

In the above equations,  stands for the frequency of the dominant allele and  stands for the frequency of the recessive allele. 

It is also important to realize that  stands for the homozygous dominant population,  stands for the homozygous recessive population, and  stands for the heterozygous population. 

We are told that 9% of the population is brown eyed, or homozygous recessive. Let's solve for .

Now let's solve for .

The question asks for the percent of the population that is heterozygous. In order to do this, we look at the first equation and plug in known values.

Thus, our answer is 42%.

Under the Hardy-Weinberg Principle, there is no change in the frequency of alleles or genotypes in a population because there are no changes to the population, such as: natural selection, mutations, migration, or chance events. In addition, mating must be random. Therefore, is it easy to see that most populations do not meet the requirements of this principle.  

For problems of this type, we need to understand the Hardy-Weinberg equations:

Here,  represents the frequency of the dominant allele, while c refers to the frequency of the recessive allele.  and  denote the proportion of homozygous dominant and recessive phenotypes, respectively. Finally, the proportion of heterozygotes is denoted by .

We already know that , and if only two alleles are present in the population,  must be equal to .

Using the values for and , we can solve for the proportion of heterozygotes using the term of the Hardy-Weinberg equation.

Gene flow occurs when new individuals of the same species are added into a population. Think of it as new genes flowing into the existing gene pool.

This influx of new genes has the potential to disrupt the allele frequency in the given population; thus, no migration (gene flow) can occur in a population in Hardy-Weinberg equilibrium.

Alleles are defined as "alternative forms of a given gene."  Though Mendelian genetics tells us that the ideal model of a gene has only two alleles, dominant and recessive, we know this is not always the case, from things like codominance (blood type) and others. Some characteristics are defined by a combination of several alleles with varying weight of expression. Alleles on autosomes are inherited from both parents, but alleles in mitochondrial DNA are inherited from the mother only. Twins are an example of organisms with identical alleles, so the answers claiming that all organisms have different alleles is false.

The first generation shows an affected father and an unaffected mother. They produce both affected and unaffected children in the second generation, meaning that the disease cannot be recessive; if it were recessive, none of the second generation could be affected due to dominant alleles inherited from the mother. We can also conclude that the affected father is heterozygous.

Knowing that the trait is dominant, we must determine if it is autosomal or sex-linked. The trait can affect females, so it cannot be on the Y chromosome. The female in the second generation is affected, even though her mother is not, meaning she must be heterozygous. If the trait is on the X chromosome, it will be passed from the affected father to all female offspring, meaning that both females in the second generation would be affected. Because one female is not affected, she must have inherited an unaffected autosomal allele from the heterozygous father.

As such, the allele for the disease must be autosomal dominant.

If an autosomal trait skips a generation, it must be recessive; however, if an autosomal trait does not skip a generation, it can be either recessive or dominant.

These concepts can be easily seen when outlined via a pedigree analysis. A dominant trait cannot skip a generation; any presence of the allele will lead to expression, thus if the trait is not expressed in a given generation, it cannot be passed down (cannot skip). A recessive allele can be masked by carriers and reappear in a later generation.

Because males only have one X chromosome, while females have two, they are more likely to be affected by a problematic X chromosome. Females can mask recessive X-linked alleles as carriers; males will express all alleles on their singular X chromosome.

Males only pass on a Y chromosome to their sons, so it is impossible for them to pass an X-linked trait to a son. Furthermore, Y chromosomes are virtually free of contributing to inheritance-linked diseases.

If only males display the disorder, it is most likely a Y-linked genetic disorder. The only possible way to inherit this disease, then, would be through the inheritance of the father's Y-chromosome.

Women have two X-chromosomes, one from each parent, and could not possibly pass down the disorder.

Epigenetic inheritance could potentially explain a genetic disorder, but, if this were the case, it should not differentiate between males and females. Abnormal testosterone levels may be a result of the disorder, but they do no explain how the disorder is inherited.