Scientists observe a newly established population of sexually reproducing plants growing on the shore of a small island. An observable trait of the plant has two possible phenotypes. It is determined by a single gene, with the dominant allele having complete dominance over the recessive allele. The first generation had 26 plants with the dominant trait and 25 with the recessive trait. The data below is from the first six generations of this population:

Generation | # of individuals w/ dominant trait | # of individuals w/ recessive trait | Total # of individuals
1 26 25 51
2 102 0 102
3 375 125 500
4 469 156 625
5 562 188 750
6 255 200 455

1) Use the data to explain the changes in phenotypic frequency from generation 1 to 3.
2) Do you think this population is in Hardy-Weinberg equilibrium? Support your answer.
3) Propose a possible explanation for the change in phenotype frequency from generation 5 to generation 6.

1) To explain the changes in phenotypic frequency from generation 1 to 3, we need to analyze the data provided. In generation 1, there were 26 plants with the dominant trait and 25 plants with the recessive trait, resulting in a total of 51 individuals. In generation 2, all 102 plants had the dominant trait, and there were no individuals with the recessive trait. By generation 3, the number of individuals with the dominant trait increased to 375, while the number of individuals with the recessive trait was 125, making a total of 500 individuals.

The change in phenotypic frequency from generation 1 to 3 can be attributed to the principles of Mendelian inheritance. In this scenario, the dominant allele has complete dominance over the recessive allele. Therefore, individuals that are homozygous dominant (DD) or heterozygous (Dd) will express the dominant trait, while homozygous recessive individuals (dd) will exhibit the recessive trait.

In generation 1, the ratio of individuals with the dominant trait to those with the recessive trait is roughly 1:1 since the population is just starting. However, as the generations progress, the dominant allele (D) is passed down more frequently thual reproduction, leading to an increasing number of individuals with the dominant trait. This trend is observed in the data, as the number of individuals with the dominant trait substantially increases in each subsequent generation.

2) To determine if this population is in Hardy-Weinberg equilibrium, we need to compare the observed phenotypic frequencies with the expected frequencies under this equilibrium. In Hardy-Weinberg equilibrium, certain assumptions need to be met, including: a large population size, random mating, no mutation, no migration, and no natural selection.

Considering the population size (ranging from 455 to 750 individuals in the given data) and the assumption of random mating, we can say that the population is not large enough for the Hardy-Weinberg equilibrium. In Hardy-Weinberg equilibrium, the population size needs to be significantly large to minimize random sampling error.

Additionally, the observed changes in phenotypic frequencies across generations suggest that there is a deviation from the expected equilibrium. The rapid increase in individuals with the dominant trait and the decline in individuals with the recessive trait indicate that one allele is being favored over the other. This could be due to natural selection or other evolutionary factors.

Thus, the population in question is not in Hardy-Weinberg equilibrium.

3) A possible explanation for the change in phenotype frequency from generation 5 to generation 6 can be understood by analyzing the data. In generation 5, there were 562 individuals with the dominant trait and 188 individuals with the recessive trait, accounting for a total of 750 individuals. However, in generation 6, the number of individuals with the dominant trait decreased to 255, while the number of individuals with the recessive trait increased to 200, with a total of 455 individuals.

This change in phenotype frequency could be a result of random fluctuations in allele frequencies due to chance events, such as genetic drift. Genetic drift is the random change in allele frequencies in a population, and its impact is more pronounced in smaller populations. Since the population size decreased from generation 5 (750 individuals) to generation 6 (455 individuals), the effect of genetic drift might have led to the observed change in phenotype frequency.

It's important to note that this change could also be influenced by other evolutionary forces, such as natural selection or migration. Further data analysis and experimental studies would be required to determine the exact cause of this change in phenotype frequency.