Question

4.Malaria is the deadliest human disease caused by any eukaryote, and as such, malaria parasites have profoundly affected human evolution and greatly impact the behaviour of modern humans.

a.Consider the allele for haemoglobin S (HbS), which is the altered haemoglobin molecule that results in sickle-cell anaemia when an individual is homozygous for the allele (HbSS).  Why does the allele for HbS persist in populations that live in regions where Plasmodium falciparum is prevalent?

Because the Plas

b.Which specific protein is at a very low frequency in populations of humans living in regions endemic for Plasmodium vivax (1 mark), and why is absence of the allele for this protein beneficial in terms of resistance to this parasite (1 mark)?

c.If malaria were globally eradicated next year, how would the frequency of the allele that codes for haemoglobin S, and the frequency of the allele that codes for that specific protein you mentioned in part b above, likely change over evolutionary time in areas that were formerly endemic for malaria?

HbS allele:

Allele that codes for protein mentioned in part b above:

d.Much optimism flows from the recent observation that bed nets are dramatically decreasing malaria prevalence in endemic regions of the world, especially Africa.  However, consider an individual living in a region endemic for malaria who has spent every evening of her first 19 years under a bed net.  On the day of her 19th birthday, the individual consumes too much beer at her friend’s house, forgets to apply insect repellent, and is now staggering home late at night.  What is one disadvantage of using bed nets as a means of avoiding P. falciparum-infected mosquitoes?

5.Coccidia are parasites of vertebrate mammals, and can be divided by life cycle into one-host coccidia, where all developmental stages occur in one host before oocysts are passed into the environment, and two-host coccidia, where parasites have exploited ecological features of predator and prey.

a.There are seven species of Eimeria that infect chickens, including the species that we covered in lecture, Eimeria tenella.  Why do you think that there are so many species of parasites in just one species of bird?

b.With regard to the infectiveness of oocysts of Cryptosporidium parvum and Cyclospora cayetanensis when they leave their host, what is the primary difference in the transmission of each species to another host?

c.Why do you think that a two-host coccidian such as Toxoplasma species evolved the requirement of an intermediate host, such as a mouse?

d.Felines are the definitive hosts for Toxoplasma species, and are the only hosts in which intestinal development of the parasite occurs.  However, development of Toxoplasma species, with resultant formation of cysts in the brain and muscles, occurs in felines as well.  Why do you think that Toxoplasma species develop tissue stages in felines?

e.You are a cattle farmer who owns five dogs.  Your herd of cattle is infected with an apicomplexan parasite, which is causing them to abort their calves at an alarming rate.  Your neighbour, Daxette Bärnstörmer, owns a cattle farm but does not have this problem, and you have noticed that she does not own any dogs.  What is the genus name of this parasite (1 mark), and how might you ensure that your cattle do not become infected with this parasite in the future (1 mark)?

9.Male gametocytes of malaria parasites differentiate in the midgut of mosquitoes to each form exactly eight male gametes.  What would you predict as the sex ratio of female gametocytes to male gametocytes in the bloodstream of humans?

A.silly Todd, gametocytes are not found in human blood!

B.there would be many more female gametocytes than male gametocytes

C.there would be equal numbers of female gametocytes and male gametocytes

D.there would be many fewer female gametocytes than male gametocytes

Answer 1

4.

a. The regions where Plasmodium falciparum is prevelent has the hemoglobin allele HbS. The prevelence of the allele in these regions is because people who are heterozygous are immune to Plasmdiun falciparum infections. So, natural selection has favoured HbS allele , that is why HbS allele survives in these parts.

b. The people living in regions endemic to Plasmidium vivax , has less Duffy antigen in the RBc membranes. This is because, Duffy antigen acts as a receptor for attaching to the Plasmodium vivax and helps the parasite in entering in to the RBCs. Natural selection has selected against this antigen. This has led to reduced frequency of this antigen or protein.

c. Evolution is a continuous process. It is a dynamic process and keeps changing based on the necessity. Because the malaria resistance increases in the presence of these alleles( HbS,Duffy antgen gene) natural selection has selected these alleles in the regions where malaria is prevelent. When the situation arises where there are no malaria cases in the population, then gradually, HbS gene will reduce in numbers. This is because, when two parents who are heterozygous to the HbS allele reproduce, there are chances of offspring being homozygous are possible. That is why frequency of the HbS will reduce over time and may not be immediate.

Duffy antigen protein also will increase in frequency because it has other important functions to perform as Chemokine receptor.

Evolution is a slow process . Based on the importance of a specific gene, selection of a particular gene varies..

d. If a person has used bed nets till the age of 19 years, then such a person may not have developed any resistance to the P.falciparum disease. When a person is exposed to the pathogen in low intensities, body will activate immune cells and develop memory cells and immune cells in the system. Such a person when exposed to larger dose fo the same pathogen will be in a position to resist the disease. But in this scenario, the person never got exposed but sudden is exposed to somany mosquitos and pathogens at the same time. So, such a person will not be able to resist the disease. Person will develop the disease.