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To fully grasp the concept of genotype frequency, imagine a great big fruit salad. Now, each type of fruit represents a genotype - a genetic makeup of an organism. In a bowl of fruit salad, the amount of each fruit present can be compared to the frequency of each genotype within a population.

In our example with the transgenic Bt corn affecting a population of corn borers, genotype frequencies refer to how common each genetic combination is within the corn borer population. Initially, we calculated the frequencies by squaring and multiplying the resistance allele and non-resistance allele frequencies. It's a bit like counting out how many apples, oranges, and pears you have in the salad to see what you're going to taste most. Genotype frequency changes when external factors, like our Bt corn insecticide, affect the survival rates of the organisms.

If we continue with our fruit salad analogy, think of allele frequency as counting the seeds of each type of fruit. Alleles are different versions of a gene, and in a population, the frequency of an allele is how many times that specific version appears compared to others.

In the initial population of corn borers, the allele frequency for the resistance gene (B) was given as 0.02. This is like saying out of 100 seeds, only 2 are from the special 'resistant' fruit. Utilizing the Hardy-Weinberg equilibrium, which assumes allele frequencies remain constant from generation to generation in the absence of other evolutionary influences, allows us to calculate the expected genotype frequencies, providing a baseline for understanding how factors such as selective pressures from Bt corn can alter the genetic makeup of the population.

Transgenic Bt corn, now that's some high-tech farming! Bt stands for Bacillus thuringiensis, a bacteria whose gene has been inserted into the corn's DNA, making it produce an insecticide. This bio-engineered corn is like a sci-fi movie star among crops because it has superpowers - it can fend off pests all by itself!

Here’s the deal: when the corn borer larvae munch on this modified plant, most find it lethal due to the Bt toxin. However, some larvae have a resistance allele, B, which is like a secret agent helping them survive this toxic dinner. Over time, as these tough little critters with their B alleles survive and reproduce more than the susceptible ones, the genetic fabric of the corn borer population begins to change.

The resistance allele (B) in our corn borer scenario is like a superpower gene. It provides the corn borers with the ability to survive the Bt corn's secret weapon. Initially, it’s rare—only present in about 2% of the population.

Consider this a genetic lottery ticket, and the corn borers with at least one copy of the resistance allele just hit the jackpot because they can withstand the Bt corn while their non-resistant comrades can't. Over generations, as these 'winner' larvae have more babies with the same lucky ticket, the resistance allele becomes more common, a clear demonstration of natural selection at work. This mirrors the way certain traits can become more frequent in a population due to conferring an advantage in survival or reproduction.