Evolution of a Population

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:

Use the data to explain the changes in phenotypic frequency from generation 1 to 3. I'm not sure how to explain the increase in the recessive trait for generation $2$ to $3$. How would a population go from $p^2+2pq=1$ to $q^2 \simeq .2$?

Do you think this population is in Hardy-Weinberg equilibrium? Support your answer. No, I don't believe so, since the population seems to change constantly in both the total number in the population, as well as the number of individuals with each trait.

Propose a possible explanation for the change in phenotype frequency from generation 5 to generation 6. Perhaps a climate change or the introduction of some new factor such as a drought or new preadator?

• You should probably take a step back and review Mendelian genetics first. It has to do with the fact that the dominant trait has complete dominance over the recessive trait. This means that while the offspring of a homozygous dominant and homozygous recessive plant will all be genotypically heterozygous, their phenotype will still be of the Dominant trait. So if Red flowers are the dominant trait and White flowers are recessive, then the heterozygous genotype will have Red flowers, and you will not be able to tell genotype from phenotype of thing individual offspring until the next generation. – AMR Aug 31 '15 at 4:27
• So let's say that all of Gen 1 is genotypical homozygous. WW for red flowers and and ww for white flowers. To get generation two all of the ww plants will have had to be pollenated by WW plants. This will lead to 100% Ww offspring for those pollinations. There could be WW offspring as well in the mix, but you cannot be certain. The only thing that you know for sure is that no ww pollenated another ww in Gen 1 because you would have seen a phenotypically recessive trait. When Gen 2 breeds, if a WW pollenates a Ww, then the 50% WW and 50% Ww, but still phenotypically red. – AMR Aug 31 '15 at 4:35
• If however, two Ww's breed, then the distribution is 25% WW, 50% Ww, 25% ww. As the 75% Red 25% White distribution in the Gen 3, then you can go back and say that all of the offspring from Gen 2 were Ww, so no WW pollenated another WW in Gen 1, besides the fact that no ww in Gen 1 pollenated a ww. I am going to leave you to think about the other questions on your own. – AMR Aug 31 '15 at 4:40