The correct answer here is AA and Aa. We can figure this out by drawing a punnet square as drawn below:

As you can see from above, there are only two options from this combination of gene alleles. If you chose any of the other options, try drawing a punnett square by placing the first parents' genes on one end of the table and the other on the top. See if you can match each allele to another one from the other parent. You should obtain the same results as above.

The question asks us to think about offspring with black horns in a trio formation. That means these offspring would be showing a recessive trait for coloration (black) and a dominant trait for arrangement (three horns). Since only one dominant allele is required for a dominant trait to "show through," the horn arrangement gene must have at least one dominant allele, which we can write as T\[ \]. However, for a recessive trait to be displayed, both alleles must be recessive: therefore, these offspring need to have ww for coloration. Thus, we are concerned with those offspring that have a genotype of T\[ \]ww– that is, offspring with genotypes TTww or Ttww.

We already are given one parent's genome in the question itself: "heterozygous for both traits" means this alien has one dominant and one recessive allele for each gene. Thus, the known parent's genotype is TtWw. We can first eliminate any answer choices that can't result in any three-black-horned babies at all. The known parent has a dominant allele for horn arrangement, meaning that there is at least some chance of this parent's children having three horns, no matter who s/he mates with. We should thus focus our energy more towards looking at the possibility of black-horned babies. If this parent mated with another alien who had only dominant genes on the coloration gene, then all their children would inherit at least one dominant gene for coloration (at least one W) and thus none would have a chance of having black horns. This means we can eliminate the choice with two dominant W's: the other parent won't be ttWW.

Next, let's consider a special situation in Mendelian genetics called a dihybrid cross. This is the mating of two parents who are both heterozygous for two traits. In this example, this mating would be our known parent (TtWw) crossed with another double heterozygote (another TtWw). The proportion of offspring phenotypes for a dihybrid cross is known to be 9:3:3:1. This means that for every 16 babies, we expect that nine will show both dominant traits; three will show dominant trait A and recessive trait B; three will show recessive trait A and dominant trait B; and one will show both recessive traits. We're concerned with those offspring that show one dominant and one recessive trait, so that means that for TtWw x TtWw, 3 out of 16 offspring will have three black horns.

From here, we probably want to look at Punnett square for the other two parent options. For a Punnett square involving two traits, we want 16 total squares representing offspring. When writing the possible allele combinations (as one allele from trait A and one allele from trait B) each parent could donate to the child, we essentially "repeat" each allele once. That is, we write the first trait A allele twice, the second trait A allele twice, the first trait B allele twice, and the second trait B allele twice. For a TtWw x ttWw cross, this looks like:

| | TtWw | | | | | | | ----------- | ---- | ------ | ------ | ------ | ------ | | ttWw | | TW | Tw | tW | tw | | tW | TtWW | TtWw | ttWW | ttWw | | | tw | TtWw | Ttww | ttWw | ttww | | | tW | TtWW | TtWw | ttWW | ttWw | | | tw | TtWw | Ttww | ttWw | ttww | |

The offspring with horns in a trio arrangement (at least one T) and black coloration (two w's) are underlined and italicized so they are easier to see. From this we can see that for TtWw x ttWw, 2 out of 16 offspring will have three black horns.

Let's do the same thing for the last answer choice for the second parent's genotype: TTww.

| | TtWw | | | | | | | ----------- | ---- | ------ | ------ | ------ | ------ | | TTww | | TW | Tw | tW | tw | | Tw | TTWw | TTww | TtWw | Ttww | | | Tw | TTWw | TTww | TtWw | Ttww | | | Tw | TTWw | TTww | TtWw | Ttww | | | Tw | TTWw | TTww | TtWw | Ttww | |

Wow! This means that for TtWw x TTww, 8 out of 16 offspring will have three black horns.

Now let's compare our options:

• TtWw x ttWW: 0/16 three black horns
• TtWw x TtWw: 3/16 three black horns
• TtWw x ttWw: 2/16 three black horns
• TtWw x TTww: 8/16 three black horns

Clearly, crossing with TTww gives the TtWw parent's offspring the best chance of have three black horns, so that is our correct answer.

The correct answer is the bottleneck effect, because this is where a natural or rare disaster wipes out an existing generation to alter the gene pool for future generations. If you chose founder effect it may have been because of the relation to bottleneck. Remember that the founder effect, however, is when the beginning population is very small resulting in a small gene pool from the start of the population. If you chose de-volution, remember that this is the opposite of progressive evolution. Famine is an example of natural disaster, however, does not equate the loss of genes

The alleles for gene A assort independently from the alleles of gene B, meaning that the genotype for one does not affect the genotype of the other. Even though there are two genes, we can solve this problem by answering the question separately for the two genes.

There are three possible genotypes with respect to the A gene (AA, Aa, aa) and three possible genotypes with respect to the B gene (BB, Bb, bb). Since genes A and B assort independently, the possible offspring will be the product of the possibilities for each separate gene.

Listed out, these genotypes are: AABB, AABb, AaBB, AAbb, AaBb, aaBB, Aabb, aaBb, aabb.

Allelic variation is a mutation in the SAME gene causing different diseases. Genetic heterogeneity is when different mutations can lead to the same disease. Variable expressivity is the varying degrees of disease with the same gene mutated. Penetrance refers to the percentage of people with a mutation that develop a disorder.

All of these are correct, true statements except choice III. Random mating indeed refers to individuals mating without choosing mates based on their traits, and this allows all alleles to be passed down to the next generation at roughly the same rate; however, in reality, organisms often show non-random preferences when choosing mates. They tend to prefer mates with traits that will make them survive longer, better able to raise offspring, more capable of protecting the family group, etc. With that said, it's clear that certain individuals have a much lower chance of successively mating—for example, if they have a genetic disorder that makes them weaker or less healthy than the average member of the species.

Since individuals choose mates non-randomly, the most reproductively fit individuals pass down their genes at a significantly higher rate than other individuals. This is also called "survival of the fittest" and is a major concept tied up with natural selection. As such, choice III is incorrect, since natural selection is essentially opposite to random mating.

Since we are given in the question that this alien population meets the requirements for a Hardy-Weinberg equilibrium, we know it is appropriate to use the Hardy-Weinberg equation to think about genotypes and phenotypes. Recall that the Hardy-Weinberg equation is:

Here, p represents the percentage of dominant alleles in the population, while q represents the percentage of recessive alleles in the population. Since all alleles in the population mustbe either dominant orrecessive, the sum of those percentages is always 1:

With that in mind, we can use the information in the question to determine that p = 0.75 and q = 0.25. The proportion of individuals that are homozygous dominant is given by p x p; that are homozygous recessive, q x q; that are heterozygous, 2 x p x q. Since rounded ear shape is dominant to pointed ear shape, we expect that homozygous dominant and heterozygous individuals will all show the rounded ear phenotype. Let's find the total percentage of those individuals that exist in the whole population:

These means 93.75% of the individuals in this population display rounded ear shape; however, this question asked for the number of individuals, so we want to multiply this proportion by the total number of individuals in the population (given as 4000):

This means that the correct answer is that we can expect 3750 of the 4000 total individuals to show rounded ear shape.

Using a punnet square, we can see that:1/4 will be red with long pedals, 1/4 will be red with short pedals, 1/4 will be white with long pedals, and 1/4 will be white with short pedals.

RL Rl rL rl

rl RrLl Rrll rrLl rrll

Human birth weight is an example of stabilizing selection, because babies that are too heavy or too light are selected against babies that are typically close to the average weight.

Founder effect is when a few individuals from a population are moved to a different environment and over generations, their genetic makeup differs from their original population.

A bottleneck effect would require most of the population to die from natural cause, instead of being moved. Independent assortment has to do with alleles and hence is not relevant. Both non-random mating and genetic drift would not cause a change in the genetic makeup of the population.