Malaria is caused by a parasite that attacks red blood cells, producing repeated bouts of serious illness and often causing death. The allele for normal haemoglobin in red cells is HbA. In the West African country of Burkina Faso, 20% of people are heterozygous for a different allele, HbC, which has no effect on their health. People homozygous for HbC suffer a very mild anaemia. The graph belowshows how the HbC allele affects the chance of getting malaria.
The HbC allele is increasing in frequency in parts of Africa, such as Burkina Faso.
The image below shows the prevalence of malaria and the frequency of the HbCallele. Those individuals homozygous with HbC HbCdevelop mild anaemia. Scientists concluded that the HbC allele is more prevalent in areas with higher risk of mortality from malaria.
Use the information inpart (a) to evaluate their conclusion.
In a village with a population of 500, there were 8 people who were homozygous for the normal adult haemoglobin sickle–cell allele and 96 who were heterozygous.
Calculate the frequency of the HbC allele in the village.
In the Earth's history there have been periods where the global temperatures have been very low. These periods can be titled as an 'ice age' or a 'glacial age'.
During these periods, the European black bear populations changed from having a small body mass, to having a much larger one.
Explain the concept of directional selection with respect to the example of black bear body mass during an ice age.
These events happened on Earth thousands of years ago, and the black bears no longer exist in Europe.
Suggest how scientists know about their evolutionary past.
[2 marks]
Question 3c
Marks: 4
c)
The phylogenetic tree below is taken from a 2008 study of the mitochondrial DNA (mtDNA) of bears and shows their evolutionary history.
i) Suggest the method the scientists used to identify which of the bears were most closely related to each other.
[1 mark]
ii) The scientists who wrote this study, Krause et al., described the findings as proving that there was a "rapid radiation" of bears 5 million years ago.
Describe the evidence from the figure that supports the idea of a "rapid radiation".
[2 marks]
iii) The brown bears and polar bears have only recently speciated when compared to the rest of the phylogenetic tree.
When a polyploidy event occurs that causes speciation, is this more likely to be an example of gradualism or punctuated equilibrium? Explain your answer.
Plants that exist in the most northern regions of the world, such as Svalbard, have been extensively studied to identify their ploidy.
The figure below shows the ploidy levels of 1719 species that were studied in different regions, ranging from warmer forested regions, north into the extreme arctic desert. 2n represent the diploid species, 4n represents the tetraploid species, and >4n represents the species with more than four sets of chromosomes.
The scientists concluded from this study that polyploidy was more common in species of plants adapted for extreme cold environments because it helps to "buffer against inbreeding".
Suggest why inbreeding is so common with these types of plants, and explain why polyploidy "acts as a buffer".
The evolution of some species can be driven by female preferences.
This has occurred in a species of birds called the long-tailed widowbird. The ancestors of the long-tailed widowbird had very short tails. This changed when females developed a behaviour causing them to preferentially mate with the males with the longest tails. However, if their tail is too long the male is weighed down by it and cannot fly, causing it to die prematurely.
Describe the type of selection that has occurred to the long-tailed widowbird.
Since the first human genome was sequenced in 2003, scientists have spent a lot of time studying human genomes around the world.
One aspect of genome study that scientists can learn a lot from is the study of the frequencies of different alleles in different populations around the world.
Explain some of the benefits of studying and comparing allele frequencies in different human populations, as well as some of the limitations of this process.
