WHAT WILL HAPPEN IN THE NEXT GENERATION?What will happen in the next generation? To answer this question, we will use the Hardy-Weinberg principle, which applies basic rules of probability to a population to make predictions about the next generation. The Hardy-Weinberg principle predicts that allelic frequencies remain constant from one generation to the next, or remain in EQUILIBRIUM, if we assume certain conditions (which we will discuss below). Show For example, if the allelic frequencies of alleles A and a in the initial population were p = 0.8 and q = 0.2, the allelic frequencies in the next generation will remain p = 0.8 and q = 0.2. The conditions for Hardy-Weinberg equilibrium are rarely (if ever) encountered in nature, but they are fundamental to understanding population genetics. When a population deviates from Hardy-Weinberg predictions, it is evidence that at least one of the conditions in not being met. Scientists can then determine why allelic frequencies are changing, and thus how evolution is acting on the population. The conditions for Hardy-Weinberg equilibrium:
 Therefore, on the paternal side (the sperm) we have the given proportions of the two alleles (0.8 of allele A and 0.2 of allele a) freely mixing with the eggs (the maternal contributions), which have the alleles in the same proportions (0.8 of A and 0.2 of a). The probability of an A sperm meeting an A egg is 0.8 x 0.8 = 0.64. The probability of an A sperm meeting an a egg is 0.8 x 0.2 = 0.16. The probability of an a sperm meeting an A egg is 0.8 x 0.2 = 0.16. The probability of an a sperm meeting an a egg is 0.2 x 0.2 = 0.04.
That is, if there were a thousand offspring, there would be:
This in turn translates to 1600 A alleles (640 + 640 + 320), and 400 a alleles (320 + 40 + 40). 1600/2000 = 0.8 and 400/2000 = 0.2; that is, the allele frequencies are the same as in the parental generation. To generalize: if the allele frequencies are p and q, then at Hardy-Weinberg Equilibrium you will have (p + q) X (p + q) = p2 + 2pq + q2 as the distribution of the genotypes.
Furthermore, the frequency of A alleles will be p2 + pq (equal to the frequency of AA individuals plus half the frequency of Aa individuals). Since p + q =1, then q = 1 - p. The frequency of A alleles is p2 + pq, which equals p2 + p (1 — p) = p2 + p — p2 = p ; that is, p stays the same from one generation to the next. The same can be shown for q. So we see that with random mating, no selection, no migration or mutation, and a population large enough that the effects of random chance are negligible, the proportion of alleles in a population stays the same from generation to generation. Let’s test your knowledge of this topic: Frequency of AA individuals: _______ Click here for an explanation: What does it mean if allele frequencies change from generation to generation in a population?So, evolution is any shift in allele frequencies in a population over generations – whether that shift is due to natural selection or some other evolutionary mechanism, and whether that shift makes the population better-suited for its environment or not.
Under what conditions will allele frequencies change in a population?Selection, mutation, migration, and genetic drift are the mechanisms that effect changes in allele frequencies, and when one or more of these forces are acting, the population violates Hardy-Weinberg assumptions, and evolution occurs.
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Condition in which the frequency of alleles in a population remains the same over generations
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