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South City High School Student BB: 16th April 2pm - Can you please explain why................... 

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Insight Into Blindness 2009 Questions Page

Jacquie Bay 11th September 2009

Thank you for the many interesting questions that you have posted here and contributed to wiki-chat.

As many of these questions as possible will be answered over the next week.  We are looking forward to your discussion on the challenges.




Alfriston College, 2 September 5pm

Page 7 states that a mutation from ATT to ACT causes the individual to be affected due to a change in one amino acid in the protein. However, when we transcribed these triplets to mRNA codons and checked the mRNA table, we found that UAA and UGA are both stop codons.

How has the protein been changed to cause this disease?


Jacquie Bay and Helen Mora 2nd September 5:45pm

Dear Alfriston,  have another look at the diagram.  The amino acid changes from Isoleucine to threonine as a result of the mutation. 

Look at the figure alone - and work out how the diagram is needs to be read to show this is the change.   Look forward to your response. 


Alfriston College Student NY: 4th September, 4:18pm

Hi,

Sorry for our confusion with mRNA synthesis, we started this topic only recently. I now understand the following:

The DNA given to us is the sense strand. It is given as ATT.

We then find its complimentary bases, TAA, this is the antisense strand.

mRNA is then made from this, and it is AUU (same as the sense strand with U
instead of T)

This is Isoleucine, and this is the amino acid which is changed by the mutation.

However, this answer only leads me to another question. How do we determine
which is the sense strand and which is the antisense strand, or, how does
the RNA polymerase determine this?



Kristin School, 4 September 9:25am F.O. & L.S. We have four questions today:

1.)Would the problem of blindness be solved if the normal protein (instead of mutated protein) was created using a vector and then inserted into affected human or does the problem need to be treated at the embryonic level?

Peter Dearden, Geneticist, University of Otago.  From the seminar

The situation you have described where you have one normal copy of the allele and one mutant, is exactly the situation that occurs in the affected female.  Because the mutation is dominant, placing a normal copy of the gene in the affected cells is not giong to be effective in overcoming the effect of the mutation.  However this is an interesting situation because in the affected female, her phenotype is not as sever as the affected male.  If you were going to use gene therapy (which is in itself a very complex process), it would indeed need to be at an embryonic level. 



Kristin School, 4 September 9:25am F.O. & L.S. We have four questions today: 

2.)Is it likely that the intellectual disabilities also observed are unrelated to the poor vision gene? If not how are they linked and therefore would too much calcium coming through the ion channel when it is meant to be closed lead to these intellectual disabilities?


Peter Dearden, Geneticist, University of Otago and Patricia Lundon-Treweek, Whanau Member From the seminar
From the evidence that we have at present, it appears highly likely that the intellectual disability is linked to the visual impairment in the males. The evidence supporting this is that only affected males are affected by intellectual disabilities; no affected females have intellectual disabilities and no unaffected males have intellectual disabilities. It is interesting to note that not all affected males have the intellectual disabilities. At the moment we do not have the answer as to what the cause of the intellectual disabilities are however it is known that the gene that is causing the visual impairment is also expressed in the brain. Further investigation of this is required to identify whether what you have suggested, the change in the behaviour of the calcium channel, is also causing the intellectual disabilities.


Marion Maw, Geneticist 12th September

In the research we showed that the gene is transcribed (expressed) in the brain’s pineal gland, which is known as the “third eye” and has an evolutionary relationship to the retina. In unpublished small-scale experiments, we were not able to detect gene activity in other parts of the brain during various stages of brain development. However it is possible that a more detailed search would obtain additional positive results. Several groups have reported the gene is active in certain cells in the immune system, raising the possibility of an indirect effect on brain development and function.


Kristin School, 4 September 9:25am F.O. & L.S. We have four questions today: 


3.)What kind of expression is this gene showing as we are a little confused as to whether it is dominant, recessive or co-dominant etc.?

Jacquie Bay 12th September 2009

This is not a simple classical inheritance pattern.  See the answer to Western Springs question below for details.



Kristin School, 4 September 9:25am F.O. & L.S. We have four questions today: 

4.)With affected people would it be possible to expose them to much brighter than normal light to close the ion channel? Or is there a way of stopping the electrical signals that cause the ion channel to open?

Peter Dearden, Geneticist, University of Otago. From the seminar 

There would be problems associated with exposing people to extremely bright light that would make this untenable. However the potential to find a biochemical mechanism by which to block the flow of calcium (a calcium blocker) is a possibility which would be worth exploring in the future.


 Kristin School, 9.09.09, 1.20pm. Dillon.

Is it the fact that the calcium gates are mostly open that means the nerve is over stimulated and so the message begins to become ignored?

Marion Maw, Geneticist.  12th September
This is an interesting question to think about, but at the moment we can really only guess as to the answer. Vision relies upon variation in light intensity (black, dark-gray, light-gray, white, ) and wavelength (different colors) being reflected from various objects in the environment into our eyes, and stimulating individual rod and cone cells to produce a “picture”. If the release of neurotransmitter were always at maximum from every cone and rod cell, then it might be like being surrounded by complete darkness. If the release of neurotransmitter were always at a minimum from every cone and rod cell, then it might be like being in the presence a very bright light (think of how it is temporarily blinding to move from a dimly lit room into bright sunshine).


Western Springs College. 10/09/0. Finn

Is this a type of Co-dominance or Incomplete dominance because in the affected females, they get better electrical signals than affected males, so would the 'normal' X chromosome 'help' with the signal.


Jacquie Bay 11th September
Co-dominance
is defined as an inheritance pattern where both alleles in a heterozygous individual contribute to the phenotype independently and in equal proportion. A well known example of this is coat colour in ROAN cattle which are the result of a cross between white and red (cow and bull). The roan has a coat made of red hair and white hair.


Incomplete dominanceis defined as an inheritance pattern where the phenotype of the heterozygous individual is an intermediate condition between the phenotype of the homozygous conditions. One allele is not dominant over the other. The well known example of this is the snapdragon flower. When a homozygous white flower plant is crossed with a homozygous red flower plant the result is a plant with pink flowers.
We know that the gene causing the eye condition in the whanau is carried on the X-chromosome. Males have one X chromosome and females two. However, only one x-chromosome is active in any cell in the female. One x-chromosome in all non-dividing somatic cells in a female is turned off (randomly) forming a barr body. Therefore in each cell in this case in the female, there is only one copy of the X-chromosome active. For this reason we cannot describe it as a classical co-dominance or incomplete dominance inheritance pattern. Rather than completely answer your question, can you use the information I have given you here to develop an answer for challenge 1? I will post more detail about the situation once people have had a chance to contribute answers to challenge 1.




WSC 10/09/09. Lucie

Lucie asks whether there are people in Spain who have this mutation for us to trace back to Jose's family or is it only here in Aotearoa?

Patricia Lundon-Treweek, Whanau Member.  From the Seminar

To the best of our knowledge, this is a mutation that is only present in the Aoteoroa branch of the family.  It appears likely that Jose was not affected because he could not have been a whaler if he was blind.  The first recorded whanau member from the research who is affected is a grandaughter of Jose (my great great grandmother). In the family tree (below) which was published in the clinical paper you can see that this is Person A in Generation III.

 Image:Familytree.gif



Zach, Horowhenua College 10/09/09

This is a personal question that I did not want to ask over the wiki chat. My grandfather became blind around 78, he has periferal vision but thats about it, a bit of background information is needed here, he faught in WWII and was one of the first on the sceen after the Hiroshima Atomic bombing (2 weeks after the bomb hit) so was exposed to large amounts of radiation which did not severly effect him at the time. All of his children and grandchildren were born fine and he is the first in our large family to exibit this blindness... I was wondering would it be possible that the radiation that he took while in Hiroshima caused this or could it be a genetic trait that could have been passed on to his children and granchildren (we celebrated his 84th birthday only this monday just gone).

Jacquie Bay 12th September

Zach - thank you for this interesting question.  I will endeavour to find someone who can talk to you about this. 


Marion Maw, Geneticist, 12th September

As they grow older, many people progressively develop vision impairment, with some individuals eventually becoming blind. For example, age-related macular degeneration, cataracts and glaucoma are common conditions amongst the elderly. If you talk with your grandfather, you may find that his optometrist or ophthalmologist has diagnosed one of these conditions. The centre of the retina contains a small region called the macula which has an extremely high concentration of cones and is responsible for high acuity vision such as that required for reading and sewing. As the name suggests, in age-related macular degeneration this region of the retina slowly dies but the remainder of the retina continues to function fairly well. Hence peripheral vision is retained. I suspect that your grandfather may have this condition, which is thought to arise from a complex interaction between genetic predisposition and environmental risk factors such as smoking and diet.

Zach Thank you for your reply. My grandfather has not smoked(as far as I am aware) and the optomitrist found the cause of the bliness is because he bleed into the back of it. If this changes anything I would love another reply. Thanks again. Zach.

Marion Maw, Geneticist, 14th September

Two common conditions in which there is abnormal growth of the blood vessels in the retina are the “wet” form of age-related macular degeneration, and retinal disease arising as a complication of diabetes. You may like to consult the following websites for more information about these conditions.

http://www.retina.org.nz/diseases/amd.htm
http://www.nei.nih.gov/health/diabetic/retinopathy.asp

Each situation is individual.  The best person to ask about this particular situation is your Grandfather's optomertrist. 

Zach - thank you for all your help much appreciated.


Zach, Horowhenua College 10/09/09
Now for my chat question. I was talking about the size diffrences between the X and the Y chromosome. Why does this not cause infertility when in some cases of trisomy 21 when the 3rd chromosome 21 joins to another chromosome such as chromosome number 14 this extends the length of the chromosome number 14 and causes the 2 chromosome number 14's to become non-homologous and causes infertility within the individual. the diffrence between the sizes of the X and Y chromosomes is about the same size as chromosome 21 so how are males able to be fertile and then those who do suffer from this form of trisomy 21 are not fertile. During normal Trisomy a cell aquires a 3rd chromosome and the person is infertile, if this is the case then how are species able to aquire new chromosome sets if whenver an individual does aquire one it becomes infertile.



Keith McGowan, Otumoetai College 15th September

As referred to in the last seminar, what is it about the mendelian pea genetics that is not 'black and white'

Peter Dearden 15th September 2009

Firstly the evidence suggests that the clear 3:1 ratios that Mendel observed are too good - some of the data looks a little fudged.
Secondly the wrinkly vs smooth peas is due to variation in sugar content in the peas.  If you measure the sugar content then it is clear that the heterozygous peas actually have intermediate levels of sugar between the two homozygote classes. So the trait, when you measure sugar content, is not dominant. This reflects the fact that dominant and recessive and all the other classes all refer to a specific part of the phenotype. What outcome you get depends very much on the part of the phenotype you look at.