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 analyze the changes in phenotypic frequency from generation 1 to 3, we need to compare the number of individuals with the dominant trait and the recessive trait in each generation.
In generation 1, there were 26 plants with the dominant trait and 25 with the recessive trait, making a total of 51 plants. The phenotypic frequency of the dominant trait can be calculated as 26/51 ≈ 0.51, while the phenotypic frequency of the recessive trait can be calculated as 25/51 ≈ 0.49.
In generation 3, there were 375 plants with the dominant trait and 125 with the recessive trait, making a total of 500 plants. The phenotypic frequency of the dominant trait can be calculated as 375/500 = 0.75, while the phenotypic frequency of the recessive trait can be calculated as 125/500 = 0.25.
Therefore, from generation 1 to 3, there has been an increase in the phenotypic frequency of the dominant trait and a decrease in the phenotypic frequency of the recessive trait. This indicates that the dominant allele is becoming more prevalent in the population over generations.
2) To determine whether this population is in Hardy-Weinberg equilibrium, we need to check if certain conditions are met. Hardy-Weinberg equilibrium assumes that there is no selection, no mutation, no migration, no genetic drift, and random mating. If any of these factors are present, the population will not be in equilibrium.
Based on the data given, we can make the following observations:
- The number of individuals with the dominant trait is increasing in each generation, indicating a possible selection advantage.
- There are changes in the phenotypic frequency over generations, suggesting that the population might not be in equilibrium.
- The total number of individuals varies from generation to generation, indicating the possibility of genetic drift or migration.
These observations suggest that this population is not in Hardy-Weinberg equilibrium.
3) The change in phenotype frequency from generation 5 to generation 6 shows an interesting trend. In generation 5, there were 562 individuals with the dominant trait and 188 with the recessive trait, making a total of 750 individuals. The phenotypic frequency of the dominant trait can be calculated as 562/750 ≈ 0.75, while the phenotypic frequency of the recessive trait can be calculated as 188/750 ≈ 0.25.
However, in generation 6, there were 255 individuals with the dominant trait and 200 with the recessive trait, making a total of 455 individuals. The phenotypic frequency of the dominant trait can be calculated as 255/455 ≈ 0.56, while the phenotypic frequency of the recessive trait can be calculated as 200/455 ≈ 0.44.
The change in phenotype frequency from generation 5 to 6 suggests a shift from the dominant trait towards the recessive trait. This change could be due to various factors such as migration of individuals with the recessive trait into the population or random fluctuations in allele frequencies caused by genetic drift. It is also possible that some sort of selection pressure favored individuals with the recessive trait in generation 6.
It would be necessary to gather more data and perform additional analysis to determine the exact reason for this change in phenotype frequency from generation 5 to 6.