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BIO 1121 week 7 written assignment unit 7
Biology 1 for Health Studies Majors (BIOL 1121)
University of the People
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Question 1: Based on this video, describe the symptoms of the SCA1 disease.
SCA1 disease affects the ability to move and balance correctly. The symptoms are progressive with age. The symptoms are loss of balance and coordination, speech and swallowing difficulties, muscle spasms and rigidity, breathing disorders. The disease finally leads to complete immobility, secondary infection and ultimately death.
Question 2: Explain how to read the chart by indicating what the squares and circles represent and what is the difference between filled and hollow shapes.
- Circles represent females and squares represent males
- A darkened circle or square represents and afflicted individual. A hollow one represented a healthy individual.
- Horizontal lines connect males and females who have parented a child
- Vertical lines connect parents to their children
- A crossed-out circle/square represents a deceased individual.
Question 3: Discuss what conclusions can be drawn from the pedigree eg assuming that the disease is caused by the mutation of one single gene, do you think this mutation is recessive or dominant? Are the affected individuals more likely to be heterozygous or homozygous for this mutation? Is the disease affecting equally men and women? For each conclusion, make sure to explain how it is supported by the pedigree.
According to the lecture, this mutation has a dominant inheritance pattern. As such, it is enough to be heterozygous to display the symptoms.
In looking at a pedigree, we are in essence analysing phenotypes and not genotypes. We therefore need to make assumptions according to what we see. We can see that it is enough to have one affected parent to transfer the disease and that about 50% of the offspring are affected. Once we see this, we can conclude that the mutation is dominant. If it were recessive, we would need to see unaffected parents transferring the mutation to their offspring. And in the case of 1 affected parent and one unaffected, we would see between 0 and half offspring affected. Or in the case of 2 un-affected parents, 25% of their offspring could have the mutation. In the pedigree we are analysing, all couples have only one affected individual with an average of 50% of affected offspring. Males and females are more or less equally affected.
Question 4: Based on the descriptions in OMIM and the information from the video, indicate what genetic mutation is responsible for the SCA1 disease and what consequence it has on protein primary structure.
According to OMIM, “spinocerebellar ataxia-1 (SCA1) is caused by an expanded (CAG)n trinucleotide repeat in the ataxin-1 gene (ATXN1; 601556) on chromosome 6p22”. When the CAG repeats lead to abnormally long ATXN1 proteins, they collect in the nucleus of the cell and do not function correctly. This leads to the cell’s death.
Question 5: Which organ and cell type are primarily affected by the mutation? Is this consistent with the symptoms observed in SCA1 patients?
The cells that are particularly affected by this mutation are the Purkinje in the cerebellum. Purkinje cells regulate and coordinate motor movement. All the symptoms observed in SCA1 patients are consistent with the destruction of the Purkinje cells.
Question 6: From the video describe the phenotype of the SCA1 mouse. Is it similar to symptoms observed in SCA1 patients?
Yes, very similar. The phenotype of the SCA1 mouse we saw in the video is one with decreased motor abilities. 2 unaffected mice and 1 affected mouse were put to balance on a rotating rod. They were timed to see how long they can hang on. The affected mouse fell of the rods much faster than the normal mice.
Question 7: Is SCA1 considered to be caused by a loss of function of the protein affected, or is it thought to be due to another mechanism?
No, SCA1 is considered to be caused by a gain of function of the protein affected. Too much of the protein results in a toxic reaction and death of the cell.
Question 8: Based on the findings from the mouse model, researchers then developed an SCA model in Drosophila – what are the advantages of using a Drosophila model over a mouse one
Drosophila flies reproduce extremely fast, they are very cheap, and are very small. It is much easier and faster to see results on these flies than it is in mice.
Question 9: Using the Drosophila model of SCA1, what was the protein kinase they found to be implicated in SCA1 associated neurodegeneration and why is this knowledge useful with respect to treating the disease?
The protein is kinase AKT. Once this is known, a pill with an inhibitor of this protein can be produced to decrease the ill effects of the mutation.
BIO 1121 week 7 written assignment unit 7
Course: Biology 1 for Health Studies Majors (BIOL 1121)
University: University of the People
