Heriditory genetic disorders.....

Paladin · 18-07-2001 10:31pm #1

Or more specifically hemophilia and colorblindness (or coloUrblindness

).

This is my attempt to add a little to this new and cool sciency board

Basically this is a query.

Im pretty well up to date on most os the chromosomal (tha a word?) possibilities of these heriditory disorders, but there are a few things that I want answered.

Drinking one night these came up briefly in conversation. A friend said that there cant be colorblind women because they are miscarried. I dispelled this myth by telling her that there ARE colorblind women, just a much smaller percentage than men (due to having a 2nd X chromosome).

Then she ammended her statement by saying that SOME miscarry because of some strange phoenomenon that causes a mother to reject the genetic deformity of colourblindness. Now this seems like awful ****e to me. How would anyone know that a miscarriage is due to colorblindness? They simply wouldnt so I simply rekon its crap, BUT I cant find any place to confirm my view. Anyone here know for certain? *cough Bob*

Question 2:

Is colorblindness increasing? All female daughters of a male sufferer will be carriers. Half female daughters of a female carrier will be carriers, and half the males will be sifferers. Does this (maths wise) mean there is an average increase?

Question 3:
Hemophilia (spelling?).
I cant find any info on the possibility of a male suffer and a female carrier having children (very very unlikely I know). Im just curious as to the outcome. Presumably this is the ONLY way for a woman to be conceived with 2 hemophiliac X chromosomes. Is THIS possibly the miscarriage my friend (mentioned earlier) was talking about?
Is there any possibility at all, however remote of a female hemophiliac surviving?
Info?

/Me ends current (and long) contribution to science

MiCr0 · 19-07-2001 9:31am

q1.
i can't see how this could be true, why wouldn't the mothers reject the son's too?

q2.
increasing? why would it be increasing?
hasn't it always been like that?

for more info:
http://www.stemnet.nf.ca/d6vsatf2000/s12/Project1/genetics.htm

bonkey · 19-07-2001 12:19pm

Originally posted by Paladin:
Q2 is based on probability mathematics (seriously ).
Its not a case of "thats how its always been".

It is either increasing, decreasing, or staying the same, and there has to be a mathematical reason for whichever it is. I dont know enough to find the answer

Well, you havent supplied enough information (I think) to work out the answer.

1) You never stated the percentages for male offspring of a male sufferer. is it 100% suffering?

2)If a female carrier (who has 50% offspring unaffected) mates with a male sufferer, what is the outcome? Which is dominant?

The argument for "how its always been" is simple. If, as a genetic trait, this is not a relatively new occurrence, then if it was on teh decrease, it would be no longer existant, or almost non-existant. Conversely, if it was on the rise, it would be predominant, as such growth rates will generally accelerate exponentially.

Ergo, without even doing the maths, I would imagine that either :

a) Color blindness is a recent genetic trait
or
b) The maths tell us that within a level of tolerance, the numbers of sufferers remains approximately constant.

Of course, I am not the medical person here, so I could be talking pants.

jc

MiCr0 · 19-07-2001 12:53pm

just checked witha geneticist (sp?)

^^ as he said

colour blindness isn't increasing, its just the population is increasing and its increasing too.

although she did say something about colour-blindness and hemophilia, but i can't remember, i'll find out though.

Paladin · 19-07-2001 5:21pm

Well the probability is like this:

Male sufferer & Female Normal:
0% male sufferer
100% female carrier.

Male Normal & Female Carrier:
50% male sufferer
50% Female carrier

Male sufferer & Female Carrier: (low probability)
50% Male sufferer
50% female sufferer
50% female carrier (0% Female normal)

Male Normal & Female sufferer: (Low prob. of female sufferer)
100% male sufferer
100% Female carrier

Male sufferer & Female sufferer (Very fuking unlikely)

100% Male sufferer
100% female sufferer

You are probably right btw Micro, tho I dont really have the knowledge to be sure.

Victor · 19-07-2001 6:22pm

Originally posted by Paladin:
A friend said that there cant be colorblind women because they are miscarried.

I suspect (but don't know) the reason for the miscarriage would be due to an adjacent gene on the chromosome which tends to be associated with the colour blindness gene). Apparently 30% of embryos are miscarried for various reasons.

I thought that the Haemophilia gene was on the Y chromosome (or is it a recessive X chromosome).

Do girls to colour blindness tests in school (we did in an all-boys school)?

Colour blindness is an advantage against conventional green-on green camouflage.

Kill, kill, kill the laser mice.

Paladin · 19-07-2001 6:44pm

Colour blindness is an advantage against conventional green-on green camouflage.

Hehe. Yeah, when I was younger and didnt know I was a little colourblind, I use wonder why the hell they called that army stuff camouflage when it stuck out like a sore thumb

Manach · 19-07-2001 9:35pm

One of my lecturers, a women, had colour-blindness. She commented it was rare but not unknown in females.

Paladin · 19-07-2001 11:30pm

Q1. - "Apparently" its so rare for women to have colourblindness that the mother simply rejects the genetic defect, but accepts it in a son because of its relatively common occurance. "Apparently", but yes you are right and Im still convinces its bull.

Q2.
There isnt any info in that link I havent seen, but thanks anyway

Q2 is based on probability mathematics (seriously

).
Its not a case of "thats how its always been".

It is either increasing, decreasing, or staying the same, and there has to be a mathematical reason for whichever it is. I dont know enough to find the answer

Victor · 23-07-2001 9:19pm

Originally posted by Paladin:

Colour blindness is an advantage against conventional green-on green camouflage.
Hehe. Yeah, when I was younger and didnt know I was a little colourblind, I use wonder why the hell they called that army stuff camouflage when it stuck out like a sore thumb 

Out of curiousity, what did it look like? Do you see all red / greens or do they just become greys?

Kill, kill, kill the laser mice.

[This message has been edited by Victor (edited 25-07-2001).]

Hannah · 24-07-2001 7:08pm

Re. Is colourblindness increasing?
Ans. no, i don't think so, this is my theory...

phenotype KEY (females):
NN = normal (homozygous)
Nn = normal (heterozygous)
nn = colourblind
(males):
N- = normal
n- = colourblind

take all possible crosses;
N N N n n n

N| NN NN N| NN Nn N|Nn Nn
-| N- N- -| N- n- -|n- n-

N N N n n n

n| Nn Nn n|Nn nn n|nn nn
-| N- N- -|N- n- -|n- n-

Results; (female) 3 normal
6 carriers (heterozygous)
3 sufferers
(male) 6 normal
6 sufferers

ratios; female 1:2:1
male 1:1

then cross the resultant individuals in the correct ratio:

N N N n (x2) n n

N|NN NN N|NN Nn N|Nn Nn
-|N- N- -|N- n- -|n- n-

N N N n (x2) n n

n|Nn Nn n|Nn nn n|nn nn
-|N- N- -|N- n- -|n- n-

results; (female) 4 normal
8 carriers
4 sufferers
(male) 8 normal
8 sufferers

ratios; (female) 1:2:1
(male) 1:1

=> ratios remain the same.
=> %age of carriers and sufferers remains the same

the thing about the colourblind girls being miscarried, i think is a mistake, the reason that there are fewer colourblind females is that the gene for colourblindness is masked in the heterozygous form in females by the dominant normal gene which is found on the part of the X chromosome which is missing in males.
however, with haemophilia, females foetuses are, afaik, always miscarried, you will never have a female haemophiliac (think about it, even if you did have a female haemophiliac she would never survive puberty, due to menstruation).

P.S. i don't mean to cause offence by refering to non-sufferers as normal etc., it's just easier to type.

Hannah · 24-07-2001 7:13pm

oops, that didn't come out very well, basically it should have read a a series of punnet tables. Anyway the results still hold.

Paladin · 25-07-2001 12:27am

(think about it, even if you did have a female haemophiliac she would never survive puberty, due to menstruation).

Actually I said that in the arguent but had my head bitten off because
[making fun of defensive woman voice]

"There isnt actually any cut, its just an old uterus being thrown out"

[/making fun of defensive woman voice]

And this still doesnt answer the question of whether a female hemophiliac could be born.

As for the maths:

<******> btw, hannah's tables are correct afaik but she came out with the wrong conclusion at teh end
<******> there would twice as many female carriers as normal females so the amount of carriers increase therefore the possibility of a colourblind child increases

Anyway, assuming your *conclusions* were right, it doesnt account for the "X" factor

Hehe. Remember the colorblind female? Now they will TOTALLY fuk up ure chart

My conclusion based purely on your chart:
There *must* be some form of overall increase (however slight). That would of course be my completely untrained conclusion based on an educated guess really

Paladin · 25-07-2001 12:44am

Out of curiousity, what did it look like? Do you see all red / greens or do they just become greys?

No it was just the green camouflage was all different shades that contrasted like something wicked making it look like a guy wearing something akin to black and yellow florescent striped on a white background

Well not THAT severe, but it was the unusual contrasts (to my eye) in totally different shades of green (some looked brown/black/orange and in some lights yellow) that stood out.

Hannah · 25-07-2001 6:29pm

there would twice as many female carriers as normal females so the amount of carriers increase therefore the possibility of a colourblind child increases

no, the comparison should be made between the results of the first cross(GI) (1:2:1) and the results of the second cross(GII) (1:2:1). The first cross simply took all the possible crosses, the actually figures are wrong because i crossed the original gametes in an incorrect ratio, the reason was just to get a sample of all the possible resultant individuals, i noted this ratio (1:2:1), then i crossed the resultant individuals in the ratio 1:2:1, this gave a result with the ratio 1:2:1, => the ratio is constant between generation I and generation II

There *must* be some form of overall increase (however slight).

not in the comparison between GI and GII, which is the comparison in question.

it doesnt account for the "X" factor

i'm not really sure what you mean by that, but the fact that there is no allele for colourblindness found on the Y chromosome in males is accounted for in the calculations because there are only 2 possible result for a male but 3 for a female - as shown in the result for males (1:1)

Remember the colorblind female?

yup, that is also accounted for in the calculations, (1:2:1), sufferers AKA colourblind females are the second "1" in the above ratio.

whether a female hemophiliac could be born.

Like pal, i'm also completely untrained and am pretty much just going on my own basic general knowledge about this, but afaik, female haemophiliacs are always miscarried early in the pregnancy, but definately the disease does not occur in females, so i'm guessing no.

Paladin · 25-07-2001 7:04pm

Actually Han I couldnt make head ass nor tail of ure chart so I honestly cant follow you.

Anyway. Hemophilia.

So females *CAN* be conceived?
If they are mis-carried why? How? Anyone?

Hannah · 25-07-2001 8:53pm

"Haemophilia is caused by a recessive gene on the X chromosome. Females with both X chromosomes carrying the recessive gene do not survive beyond the first 4 months of life in the womb." Senior Biology, Siobhán Scott.

It's only a LC book and it doesn't go into detail about the mechanism of the miscarriage or the reasons why. I'm not sure if something happens to the foetus itself or if it is rejected by the mother, but the way it's written, to me, implies that the problem is with the foetus.
Also, i think there my be a form of haemophilia which is acquired later in life, and to which both males and females are susceptable. There are also other bleeding diseases which effect males and females eg.
Von Willebrand's disease.

Victor · 25-07-2001 9:54pm

Hannah, you can reconstruct your tables by editing your post and replacing " " (2 spaces) with " ." (space .). click on "submit now" and repeat process until you have it about right.

UBB (the application that runs boards.ie) doesn't really like multiple spaces or tabs.

Kill, kill, kill the laser mice.

Victor · 25-07-2001 9:56pm

Originally posted by Victor:
Hannah, you can reconstruct your tables by editing your post and replacing " " (2 spaces) with " ." (space .). click on "submit now" and repeat process until you have it about right.

UBB (the application that runs boards.ie) doesn't really like multiple spaces or tabs.

Is haemophilia associated with colour blindness?

Kill, kill, kill the laser mice.

Hannah · 27-07-2001 5:58pm

Hannah, you can reconstruct your tables by editing your post and replacing " " (2 spaces) with " ." (space .). click on "submit now" and repeat process until you have it about right.

yes, yes i could if i wasn't quite so lazy

Is haemophilia associated with colour blindness?

only in so much as it's an X-linked gene, i spose they are on the same chromosome and that would mean that they are linked and therefore transmitted together, possibly, but afaik it's not a common linkage, so in conclusion, i'm not sure

MiCr0 · 27-07-2001 6:54pm

latest i've heard....

CB'ness and haemaphilia might be releted.
research is ongoing in the usa, i'll post a link on monday.

Victor · 31-07-2001 6:12pm

Originally posted by Hannah:
only in so much as it's an X-linked gene, i spose they are on the same chromosome and that would mean that they are linked and therefore transmitted together, possibly, but afaik it's not a common linkage, so in conclusion, i'm not sure

Fine, thanks. It's not like if you have one you will invariably have the other (be that carrier or sufferer)

Kill, kill, kill the laser mice.

Hannah · 31-07-2001 7:01pm

It's not like if you have one you will invariably have the other

yep, and even though i think they are linked (?) the odds of either suffering from or carrying both haemophilia and colourblindness are probably pretty slim, but again, i stress, i'm really not sure.

Victor · 06-08-2001 5:29pm

Hannah, if you want a table use the UBB as follows [c ode]table[/c ode] (delete the spaces in the word code). be aware that code does not use character return and makes the page really wide (I have edited it here).

Originally posted by Hannah:
[b]
Re. Is colourblindness increasing?
    Ans. no, i don't think so, this is my    theory... 

phenotype KEY (females): 
               NN = normal (homozygous)
               Nn = normal (heterozygous)
               nn = colourblind
              (males):
               N- = normal
               n- = colourblind

take all possible crosses;
   N   N           N   n         n   n
  -------         -------        -------  
N| NN  NN       N| NN  Nn      N|Nn  Nn  
-| N-  N-       -| N-  n-      -|n-  n-


   N   N           N    n        n    n
  -------         ---------     ---------
n| Nn  Nn        n|Nn   nn     n|nn   nn
-| N-  N-        -|N-   n-     -|n-   n-

Results; (female) 3 normal
                  6 carriers (heterozygous)
                  3 sufferers
         (male) 6 normal
                6 sufferers

ratios; female 1:2:1
        male 1:1

then cross the resultant individuals in the correct ratio:

  N   N             N   n  (x2)   n   n
 --------          --------      ----------
N|NN  NN          N|NN  Nn      N|Nn  Nn
-|N-  N-          -|N-  n-      -|n-  n-

  N   N             N   n  (x2)   n    n
 --------          --------     --------- 
n|Nn  Nn          n|Nn  nn      n|nn   nn
-|N-  N-          -|N-  n-      -|n-   n-   

results; (female) 4 normal
                  8 carriers
                  4 sufferers
         (male) 8 normal
                8 sufferers

ratios; (female) 1:2:1
        (male) 1:1

=&gt; ratios remain the same.
=&gt; %age of carriers and sufferers remains the same

the thing about the colourblind girls being 
miscarried, i think is a mistake, the reason
that there are fewer colourblind females is
that the gene for colourblindness is masked
in the heterozygous form in females by the
dominant normal gene which is found on the
part of the X chromosome which is missing
in males.

however, with haemophilia, females foetuses
are, afaik, always miscarried, you will
never have a female haemophiliac (think
about it, even if you did have a female
haemophiliac she would never survive
puberty, due to menstruation).

P.S. i don't mean to cause offence by
refering to non-sufferers as normal etc.,
it's just easier to type.[/b]

Kill, kill, kill the laser mice.

[This message has been edited by Victor (edited 06-08-2001).]

[This message has been edited by Victor (edited 06-08-2001).]

Hannah · 06-08-2001 9:05pm

aw thanks victor, you're so nice!,
(it probably doesn't make any sense now after all)

Victor · 08-08-2001 5:50pm

You are welcome.

/me has dirty big grin on his face.

Kill, kill, kill the laser mice.

azezil · 10-08-2001 2:07pm

oh god no Hannah stop that! ahhhh flash backs of secondry school biology! ahhhhhhh

"just because you're not paraniod, doesn't mean they're not after you!"

Bob the Unlucky Octopus · 13-08-2001 9:38am

Colorblindness is not linked in any way to hemophelia as far as we know. Such rumors used to circulate amongst the royal families of Europe, where hemophelia was a serious problem for many. What is most likely responsible, is that colorblindness has always been relatively common in the human gene pool. The current popular theory is that in recent times(geologically speaking), chromatic distinction became a disadvantage, especially during the ice age.

Having significantly more rods than cones in one's retina allows for better night-vision, and also diminishes snow/ice glare. In other words, it used to be an evolutionary advantage- but in today's day and age, where aesthetic values far outscale those of survival, it becomes something that people notice.

Hannah, you are absolutely correct about hemophilia not presenting in female adults. The reason is, that autosomal nucleon recessive disorders such as the hem/haemophelias are usually doubly expressed in female embryos.

As a result, during the third month of pregnancy, when the circulatory system begins to develop from a self-circumventing tube, the defective gene is responsible for the embryo being unable to grow to a sufficient size, and because of an inability to manufacture either spleen or thymus, a complete dearth of antibodies.

After a while, the mother's immune system attacks the embryo, treating it as a multicellular parasite.

Bob the Unlucky Octopus
(btw Hannah, nice tabulation there of a dihibrid cross- very well explained indeed

)

Hannah · 13-08-2001 9:00pm

hey bob, (or anyone who happens to know) i have a question, if the genes for colourblindness and haemophilia are both X-linked and therefore both occur on the same chromosome (?), why are they not linked?,

Bob the Unlucky Octopus · 14-08-2001 8:11am

Because it's entirely possible for one mutation to exist on an X-chromosome independent of another. There are hundreds and hundreds of X-linked conditions. Put simply, they are on different parts of the X-chromosome. They don't cross over normally, and c-19 strands don't exist on sex chromosomes.

So I could have a faulty gene related to hemophelia, but not have the colorblindness trait. Or vice-versa. A chromosome contains millions of base-pairs, and thousands of genes, several linked to conditions, and most of them independent of each other. Hope that helps

Bob the Unlucky Octopus

Hannah · 14-08-2001 7:27pm

hhhhhmmmmm,
"Put simply, they are on different parts of the X-chromosome.",
but they're on the same chromosome?, isn't that what "linked" means?

is it that they are a part of the X chromosome as opposed to the tail of the Y chromosome?
also, what's a c-19 strand?

Bob the Unlucky Octopus · 15-08-2001 11:25pm

Ahhhhh...I see what might be the problem- you seem to be confusing the term "X-linkage" with the linkage of two conditions. If a condition is X-linked, that means that it has a strongly expressed X-chromosomal component. Ie- it's more likely to be expressed strongly in men as they only have one X chromosome- with women acting as carriers. Both hemophilia and colorblindness traits are X-linked.

If two conditions are linked (such as cystic fibrosis and alveolar polycystaemia), it means that the expression of one condition is often accompanied by the other. Very often, if one of the faulty genes is expressed, so will the other. However, hemophilia and colorblindness are not linked to each other. Linked to the X chromosome, but not to each other. Does that make it any clearer?

Bob the Unlucky Octopus

Heriditory genetic disorders.....

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