Observations: When Malaria is present and infects red blood cells, parasites can infect cells carrying defective hemoglobin which may result in death. Allele frequency changes over time depending on the pressures or circumstances facing a particular population. African populations are especially impacted by both malaria and sickle cell anemia. Depending on the impacted population, allele frequency often shifts and well suited organisms are likely to survive and allele frequencies can increase.
When a population is effected by disease or other circumstances, allele frequency may decrease or change. HbA (normal hemoglobin) and HbS (defective hemoglobin) have varying frequencies and while the HbS gene is present in populations it is important to understand how Malaria in particular can affect the sickle cell frequency. The way that diseases such as malaria impact the HbS gene may be different than how populations unaffected by malaria are impacted by HbS. What will happen to the sickle cell frequency in the presence of Malaria? Hypothesis: : In the presence of malaria, the sickle cell allele frequency HbS will decrease and HbA allele frequency will increase in African populations. 2. In the presence of malaria the sickle cell allele frequency HbS increases and HbA frequency decreases in African populations. Experiment: I would test hypothesis one by first labeling paper cups “HbA/HbA,” “HbA/HbS,” “HbS/HbS,” “non-surviving alleles,” and “African population. ” I would place 75 red beans (HbS) and 25 white beans into the cup labeled “African population” and will randomly choose two beans at a time until all of the beans are gone.
If the pair has HbA/HbA then I will flip a coin (50% chance) to determine whether the population will contract malaria. Heads, the “child” has malaria and tails, they are healthy. If the pair or alleles have malaria then I will put those beans into the cup labeled “non-surviving alleles. ” For all of the pairs that do not have malaria, I will place them into the HbA/HbA sack or HbA/HbS sack. I will continue my experiment by recording how many HbA and HbS alleles survived in this generation.
I will record this data and calculate the percentages so that my frequency for each HbA and HbS add up to 1. Predicted Results: If hypothesis 1 is true, and sickle cell allele frequency decreases and the HbA allele frequency increased And I test this hypothesis by picking red and white beans out of a sack at random in order to simulate and determine the HbS and HbA surviving allele frequencies Then the sickle cell allele frequency HbS will decrease and HbA frequency will increase.
If hypothesis 2 is true and sickle cell allele frequency increases and HbA frequency decreases And I test this hypothesis by selecting red and white beans out of a sack at random in order to determine the HbS and HbA surviving allele frequencies Then the sickle cell allele frequency HbS will survive and have an increased frequency while HbA allele frequency will decrease. Data Tables: “Frequency of HbA” = 100 x [79/(79+15)] “Frequency of HbS” = 100 x [15/(15+79)] F1 Generation Surviving Alleles |
Number of surviving HbA alleles | 79| Number of surviving HbS alleles | 15| F1 Generation Surviving Allele Frequency (added together these two figures must equal 100%)| Frequency (%) of HbA alleles | 84%| Frequency (%) of HbS alleles | 16%| F2 Generation Surviving Alleles | Number of surviving HbA alleles | 75| Number of surviving HbS alleles | 11| F2 Generation Surviving Allele Frequency(added together these two figures must equal 100%)| Frequency (%) of HbA alleles | 87%| Frequency (%) of HbS alleles | 13%| Summary:
If hypothesis 1 is true, and the sickle cell HbS allele frequency decreases and HbA gene frequency increases And I test this hypothesis by picking red and white beans out of a sack at random in order to simulate the HbS and HbA surviving allele frequencies Then the sickle cell allele frequency HbS will have a low frequency and HbA allele frequency will increase AND if after conducting the experiment and comparing the results, HbS allele frequency has decreased and HbA frequency increases Therefore my hypothesis is supported
If hypothesis 2 is true and sickle cell allele frequency increases while HbA gene frequency decreases And I test this hypothesis by selecting red and white beans out of a sack at random in order to determine the HbS and HbA surviving allele frequencies Then the sickle cell allele frequency HbS will survive and have a high frequency while HbA frequency will decrease BUT if after conducting the experiment, the HbS allele frequency has not increased and HbA frequency has not decreased THEREFORE my hypothesis is not supported
One of the core biological concepts discussed in this lab is Natural Selection. In this lab, I learned that individuals who are homozygous for HbS have a significant disadvantage in terms of their ability to survive. It is also evident that when Malaria impacts a population, the most “fit” alleles (those that are heterozygous) survive at a higher rate because they have some resistance to malaria. Natural selection is a core biological concept expressed in this experiment and it is highlighted in the fact many of the HbS alleles do not survive throughout the generations.
Additionallu HbS frequency decreases after a malaria outbreak impacts a population while HbA frequency actually increases throughout the generations. In my daily life the core concept of natural selection as it pertains to HbS and HbA alleles is important because I can share the knowledge of what I have learned with my younger brother who is currently in Africa with a group of students conducting health clinics for the various populations in the country.
He is focused on children’s oral health care but it is useful for him to know the impact that malaria and HbS allele has on the population that he serves. The prevalence and frequency of HbA alleles, HbS alleles, and malaria is of constant concern for my brother who is serving the African population and this lab helped me to understand that it is an even greater concern for the people in the country. Over the course of the experiment the HbA and HbS allele frequency changed.
The parent alleles had frequencies of 75% (HbA) and 25% (HbS) respectively and in the F1 generation the HbA frequency increased to 84% and HbS dropped to 16%. In the F2 generation the allele frequency shifted even more as the HbA frequency increased to 87% and HbS frequency decreased to 13%. With the parent frequencies, HbA frequencies, and HbS frequencies in mind for the to entire experiment the over all trend for each allele frequency is that HbA increased by a few percentage points and HbS frequency decreased through the generations by a few percentage points.
Although individuals born with sickle cell anemia (HbS/HbS) are unlikely to live on to reproduce, the HbS allele still lives on through the generations for a few reasons. As we see in the experiment there is a 50% chance that each time a double HbS set of alleles is drawn from the cup will survive. That means that 50% of the alleles don’t survive but there are some that do go on to live and pass through the generations.
Additionally, in places like Africa where malaria is more common and present in the population, and the climate is warm, those who are heterozygous for the HbS allele have a better chance of resisting malaria so the gene actually turns into a survival mechanism. In Africa those with a single HbS gene are more resistant to malaria so people of that population actually benefit and can survive better by having heterozygous alleles for HbS and HbA. In the United states, malaria is not a disease profoundly effecting the population so it is more detrimental for an individual to have one HbS gene that can potentially be passed on.
