5.04 Honors: Population Change: Field Excursion

The Honors student will:

• identify phenotypes based on genotypes
• predict and compare genotype frequencies over time
• learn about the Hardy-Weinberg Equilibrium and how we can apply it to learn about populations
• identify the conditions necessary to reach and maintain the Hardy—Weinberg Equilibrium

The work of Godfrey Hardy and Wilhelm Weinberg examines the distribution of alleles in a population or the population’s gene pool.

The Hardy—Weinberg principle states that if conditions remain the same the both the gene frequency and genotype frequency in the population will remain constant.

When this happens, we call this the Hardy—Weinberg equilibrium. This helps us explain why recessive genes do not disappear from populations and how alleles are distributed within populations. It will help us predict what our population of lady bugs will look like today. 

Take a look at this Hardy-Weinberg animation from Oklahoma State University. This makes it easy to see how these 5 conditions can change how alleles are distributed in a population.

Oklahoma State: Department of Zoology

Making Predictions

The Captain has just informed me that we are all tied up and ready to go ashore! This will be fun. We can get take our tour and then head back to the boat where we will  make a prediction of what portion of the island’s current population of ladybugs will be solid red in color, solid black in color, or have spots.

I contacted the team at the research station and they are sending out a field scientist meet us so we can get a sample size and a count of individuals of each color in the sample. We know we have a large population so we are going to do a count on 1000 ladybugs.

Using the Hardy-Weinberg principle and our knowledge of genotypes and phenotypes we can predict the genetic makeup, or the gene pool, of populations. By knowing the genetic makeup of the individuals in a population, we can determine their phenotype or what traits will be visible.  I wonder why they look different.

What do we need to know in order to make this prediction?

Genes make up DNA which holds all the genetic information that is needed for an individual. Genes can vary. The different forms a gene can take are commonly called alleles.

Need genetics review?

Our Ladybugs alleles are:

• D—Dominant (black)
• d—Recessive (red)
• Dd—Codominance (spotted)

It is time to get some important background information.

Now, read our field notes.

Visit the link below to learn more about the Hardy- Weinberg Equilibrium and the forces of evolution that are required.

Hardy—Weinberg Activity

Making comparisons. We have a problem!

We wanted to compare populations from years ago to today’s population. When we were on the island I asked that they give me a call with this information. I just heard from them and it turns out that much of the information about the founding population had been lost.  There was a flood last year and many records were damaged.  All they had recorded was that the original population had 20% dominant alleles.

If we know allele frequency can we figure out phenotypes?

Let’s see what we can figure out if we use the Hardy-Weinberg Equation. It tells us that genotype frequencies will remain constant if there is a stable environment.  This can help us discover how alleles are distributed in a population.  When phenotypes are known we can use the equation to predict genotypes.

The Hardy—Weinberg Equation
p2 + 2pq + q2 = p + q

p = dominant alleles

q = recessive alleles

Let's learn how we can use this equation to find out about our founders population. What the following Hardy—Weinberg Equation Presentation or read the text version.

Now that we have used the equation to figure out the exact numbers of each color the founding population has let’s compare our field count of today’s population and see if the population has changed over time.

Can you believe it! What is going on? We must not have met the conditions for the Hardy—Weinberg equilibrium if our population has changed.

We better go back and look at the 5 conditions that were necessary for the Hardy—Weinberg Equilibrium and see what could have changed the outcome for our population of ladybugs. A text version of this review is also available.

Can you believe how many things can affect a population‘s gene pool? It is no wonder Darwin’s observations lead him to conclude that living things evolve or change over time.

Our ladybug population was interesting to look at. We concerned ourselves with only one specific trait, color, and determined that there were many events that disrupted the chance for the Hardy—Weinberg equilibrium. We proved that the population of lady bugs on the islands is evolving because of the difference in allele distribution for color.