Q4ITD
Question
Calculate the observed frequencies of genotypes CGCG, CGCY, and CYCY at day 21. Compare these frequencies to the expected frequencies calculated in question 2 and to the observed frequencies at day 7. Is the seedling population in Hardy-Weinberg equilibrium at day 21, or is evolution occurring? Explain your reasoning and identify which genotypes, if any, appear to be selected for or against.
Step-by-Step Solution
VerifiedThe observed genotype frequencies of the genotypes \({C^G}{C^G}\), \({C^G}{C^Y}\), and \({C^Y}{C^Y}\) at day 21 are 0.27, 0.61, and 0.12, respectively.
The observed genotype frequencies at day 21 for each seedling differ from the observed and expected genotype frequencies at day seven. Thus, the allele frequencies have changed from day seven till day 21.
The seedling population is not in Hardy-Weinberg equilibrium at day 21 and is undergoing evolution.
The seedling population is not in Hardy-Weinberg equilibrium at day 21 because the observed and expected genotype frequencies for both the homozygous dominant and recessive genotypes are different from day 7. The genotype \({C^G}{C^G}\)is being selected for, and the \({C^Y}{C^Y}\)is being selected against evolution.
A Hardy-Weinberg population has a similar observed and expected genotype frequency throughout. If genotype frequency changes, it implies that selection is acting for or against a particular allele or genotype. Genotype selection causes certain genotypes to survive, reproduce, and flourish than the other genotypes in a population.
To calculate: Observed frequencies of genotypes \({C^G}{C^G}\), \({C^G}{C^Y}\), and \({C^Y}{C^Y}\)at day 21.
On day 21,
Number of homozygous dominant or green seedlings (\({C^G}{C^G}\))= 47
Number of heterozygous genotypes or green-yellow seedlings (\({C^G}{C^Y}\))= 106
Number of homozygous dominant or yellow seedlings (\({C^Y}{C^Y}\))= 20
Total number of seedlings= 173
The observed genotypic frequency of \({C^G}{C^G}\) (\({p^2}\)) is:
\({p^2} = \frac{{Number{\rm{ }}of{\rm{ }}homozygous{\rm{ }}dominant{\rm{ }}or{\rm{ }}green{\rm{ }}seedlings{\rm{ }}\left( {{C^G}{C^G}} \right)}}{{Total{\rm{ }}number{\rm{ }}of{\rm{ }}seedlings}}\)
\(\begin{aligned}{l}{p^2} &= \frac{{47}}{{173}}\\{p^2} &= 0.27\end{aligned}\)
The observed genotypic frequency of \({C^G}{C^Y}\) (\(2pq\)) is:
\(2pq = \frac{{Number{\rm{ }}of{\rm{ }}homozygous{\rm{ }}dominant{\rm{ }}or{\rm{ }}green{\rm{ }}seedlings{\rm{ }}\left( {{C^G}{C^Y}} \right)}}{{Total{\rm{ }}number{\rm{ }}of{\rm{ }}seedlings}}\)
\(\begin{aligned}{l}2pq &= \frac{{106}}{{173}}\\2pq &= 0.61\end{aligned}\)
The observed genotypic frequency of \({C^Y}{C^Y}\) (\({q^2}\)) is:
\({q^2} = \frac{{Number{\rm{ }}of{\rm{ }}homozygous{\rm{ }}recessive{\rm{ }}or{\rm{ }}yellow{\rm{ }}seedlings{\rm{ }}\left( {{C^Y}{C^Y}} \right)}}{{Total{\rm{ }}number{\rm{ }}of{\rm{ }}seedlings}}\)
\(\begin{aligned}{l}{q^2} &= \frac{{20}}{{173}}\\{q^2} &= 0.115\\{q^2} &= 0.12\end{aligned}\)
Thus, the observed genotype frequencies of the genotypes \({C^G}{C^G}\), \({C^G}{C^Y}\), and \({C^Y}{C^Y}\)at day 21 are 0.27, 0.61, and 0.12, respectively.
To compare the observed genotype frequencies at day 21 to the observed and expected frequencies of genotypes \({C^G}{C^G}\), \({C^G}{C^Y}\), and \({C^Y}{C^Y}\)at day 7.
The observed genotype frequencies of the genotypes \({C^G}{C^G}\), \({C^G}{C^Y}\), and \({C^Y}{C^Y}\) at day 21 are 0.27, 0.61, and 0.12, respectively. The observed genotype frequencies of the genotypes\({C^G}{C^G}\), \({C^G}{C^Y}\), and \({C^Y}{C^Y}\)at day 7are 0.23, 0.51, and 0.26, respectively.
The expected frequencies of the genotypes\({C^G}{C^G}\), \({C^G}{C^Y}\), and \({C^Y}{C^Y}\)are 0.23, 0.50, and 0.26, respectively.
The observed genotype frequencies at day 21 for each seedling are different from the observed and expected genotype frequencies at day seven. Thus, the allele frequencies have changed from day 7 to day 21.
The comparison between the observed genotype frequencies at day 21 and observed and expected frequencies of genotypes \({C^G}{C^G}\), \({C^G}{C^Y}\), and \({C^Y}{C^Y}\)at day seven suggests that the seedling population is not in Hardy-Weinberg equilibrium at day 21 and is undergoing evolution.
The seedling population is not in Hardy-Weinberg equilibrium at day 21 because the observed genotype frequency for each seedling is different compared to the observed and expected genotype frequencies at day 7.
The genotype frequency for\({C^G}{C^G}\)has increased to 0.27 on day 21 from 0.23 as observed on day seven. On the other hand, the genotype frequency for\({C^Y}{C^Y}\)has decreased at day 21 from 0.26 to 0.12.
On day 27, many \({C^Y}{C^Y}\)plants were not surviving. The population of \({C^Y}{C^Y}\)plants fell from 56 to 20 while \({C^G}{C^G}\) plants were decreased slightly and were stable. Thus, the genotype \({C^G}{C^G}\)is being selected for, and the \({C^Y}{C^Y}\)is being selected against evolution.