Navigating the Complexities of Heterozygosity in Laboratory Rats

In a population of laboratory rats, if 49% have black fur and the rest are agouti, what percent is likely heterozygous for the fur trait?

• A. 21%
• B. 35%
• C. 42%
• D. 56%

Answer: (C)

To understand the percentage of the population likely heterozygous for the fur trait, we can apply the Hardy-Weinberg principle. This principle helps predict genotypic frequencies in a population that is in equilibrium with respect to certain conditions. Given that 49% of the rats have black fur, we can denote the frequency of the black fur phenotype as 0.49. Since black fur is typically dominant over agouti fur, we can assume that this phenotype arises from both homozygous dominant (BB) and heterozygous (Bb) individuals. The agouti phenotype (bb) comprises the rest of the population, which is 51% (100% - 49%). In a population in Hardy-Weinberg equilibrium, the frequencies of the genotypes can be defined as: - p^2 for homozygous dominant (BB) - 2pq for heterozygous (Bb) - q^2 for homozygous recessive (bb) Here, we denote: - p = frequency of the dominant allele (B) - q = frequency of the recessive allele (b) Since homozygous recessive rats correspond to the agouti phenotype, we know that q^2 is 0.51

Ever scratch your head over the genotypic frequencies in a lab full of rats? You’re not alone! Understanding the genetic makeup of organisms can be as perplexing as piecing together a jigsaw puzzle with missing pieces. But fear not! Let's break it down together as we explore the fascinating world of heterozygosity in laboratory rats, particularly when it comes to their fur color.

Let’s start our journey with a basic question: if you had a population of rats, where 49% sport black fur, what do you think the chances are that a randomly selected rat will be heterozygous for that trait? Ah, the thrill of statistics! If you’re picturing percentages dancing in your head, you’re on the right track. The answer in this case is a solid 42%. But how do we get there? Grab your thinking cap and let’s unpack this.

This is where the Hardy-Weinberg principle struts its stuff. You might have heard about this gem before—it helps us understand genotype frequencies within a population that’s sitting pretty in equilibrium under certain conditions. Think of it as the calm before the evolutionary storm! Here’s the scoop: when we denote the frequency of the black fur phenotype, we note it at 0.49. Since black fur is the dominant trait (think of it as the life of the party), it can be present in both homozygous dominant (BB) and heterozygous (Bb) individuals. The remaining agouti phenotype, or bb, makes up 51% of our furry population because, (spoiler alert!) 100% minus 49% equals 51%. Science at its finest!

Now, in Hardy-Weinberg equilibrium, we can calculate the genotype frequencies. They are expressed as p² for homozygous dominant (BB), 2pq for heterozygous (Bb), and q² for homozygous recessive (bb). So, if we denote ‘p’ as the frequency of the dominant allele (B), and ‘q’ as that of the recessive allele (b), here’s where the math gets serious.

Knowing that the agouti rats comprise the q² section of this equation, we plug in what we know:

1. q² = 0.51 (for those adorable agouti rats).

2. To find q, let’s take the square root of 0.51. This leads us to about 0.714, or 71.4% (breathe, this is just the beginning).

3. Now, since p + q = 1, we can derive that p = 1 - 0.714, which gives us p = 0.286 or approximately 28.6% (we’re almost there!).

4. Now, let’s throw this into the equation for heterozygous frequency, 2pq. This leads us to 2 * 0.286 * 0.714, which rounds out to about 0.42, or 42%.

And just like that, you've traveled down the rabbit hole of genetics and emerged with a clearer understanding. The whole world of genetics can often feel like a wild jungle, but equipping yourself with tools like the Hardy-Weinberg principle can give you the insight you need to conquer the challenges that emerge.

Why is this important? Understanding these concepts can really help you in exams like the USA Biology Olympiad (USABO). So, whether you’re cramming in the last few hours or deep in the study grind, remember: genetics might have its complexities, but it’s also bursting with fascinating insights that illustrate the beauty of life on this planet. Now, get ready to ace that exam and impress your peers with your newly-gained genetic knowledge!