HELP!! Science / Math Question

[newkris]

ok, since you guys got me through math quite well. . . . here's a biology/math question for you.

IF AA is the genotype for the non-sickle and aa is the genotype for sickle cell AND Robert's parents are Aa and Aa (unaffected heterozygous) then does that make Robert's probability of being a carrier 2/3?

IF Mary's parents are AA and A_ (mother is a carrier, father is not) and her grandmother is A_ with a sister who is aa . . . does that make Mary 4/9 probability of being a carrier?  (2/3 for her mother, 2/3 for her grandmother multiplied by each other)

AND then . .. would that make their child likely to be 8/27 (2/3 times 4/9)?

does anyone know what i'm talking about?  and does my rationale make sense?

these are questions on my exam with the answers i have come up with, but since i have only randomly (my favorite word, ) come up with the right answers for every probability question presented in this course, i thought i'd see if this time i'm right or wrong or if anyone knows.

so.  my medical scientific math brained friends . . .  what do YOU think? 

[Chseeads]

[MelodyB]

I think you are on the wrong board.

[newkris]

this is my life in college.  someone HELP me get through this last exam or i'll be stuck in college life until i'm 96.  which isn't that far away, i guess . . .

[The Purple Fuzzy]

Too bad Chels at work, she might be able to help.

[MelodyB]

I'm sorry Kris...this is NOT my department! AT ALL!

[newkris]

i have until friday to post it so maybe by then some superintellectualmedicalmathematicalscientific friend will come along and rescue me. 

[taco_harvell]

Can you ask the question again in English? lol

I have no clue....

[The Purple Fuzzy]

Dina was working on it, so she may be back to post.

[CDAGeek]

I'm working it out now, I'll post again later on tonight.

[The Purple Fuzzy]

Hooray for da Geek!

[nicolejoy]

think of it like this - if you have a general "AB" from mum and "CD" from Dad, there are always 4 possible outcomes. AC, AD, BC and BD. You can think about it like this:


        Mum  A     B
Dad
C             AC    BC
D             AD    BD

In your situation though, both parents are Aa so the little "table" will look like this:

        Mum  A     a
Dad
A             AA    Aa
a             Aa    aa

ALL of the probabilities should be out of 4 - so the likelihood of AA is 1/4, aa is 1/4 and Aa is 2/4 or 1/2

[CDAGeek]

ok, since you guys got me through math quite well. . . . here's a biology/math question for you.

IF AA is the genotype for the non-sickle and aa is the genotype for sickle cell AND Robert's parents are Aa and Aa (unaffected heterozygous) then does that make Robert's probability of being a carrier 2/3?

The possible genotype's that Robert would inherit would be AA, Aa, aA, or aa. Out of the four, three of them cause him to be a carrier. In probabilities you can't necessarily combine the two genotypes that have the same inherited gametes, as they represent the trait coming from different parents, each of which have a chance of happening.

IF Mary's parents are AA and A_ (mother is a carrier, father is not) and her grandmother is A_ with a sister who is aa . . . does that make Mary 4/9 probability of being a carrier?  (2/3 for her mother, 2/3 for her grandmother multiplied by each other)

I'm not sure how the grandmother's information is relevant here. We know one parent is AA (IE, not a carrier) and one is A_. We also know one of the parents is a carrier. Therefore the father has to be AA, and the mother Aa (otherwise neither would be a carrier). This leads to Mary having a probability of 2/4 (AA, Aa, AA, Aa).

AND then . .. would that make their child likely to be 8/27 (2/3 times 4/9)?

If you work out the charts for all the possible combinations from what we did above, that gives a total number of combinations at 48, with 24 of them resulting in the child being at least a carrier, which simplifies to 1/2.

does anyone know what i'm talking about?  and does my rationale make sense?

these are questions on my exam with the answers i have come up with, but since i have only randomly (my favorite word, ) come up with the right answers for every probability question presented in this course, i thought i'd see if this time i'm right or wrong or if anyone knows.

so.  my medical scientific math brained friends . . .  what do YOU think? 

Hope this helps!

[nicolejoy]

Here's a graph I found:



This kind of heredity is called autosomal recessive inheritance... where both parents are "carriers" but unaffected

[nicolejoy]

One thing to check if you're on the right track, all the probabilities should be out of 4... All the info about grandmother etc are just to give you more information. You may need to make up two different "tables" if you don't know if the parent is a carrier or not though... but the table I showed you, I think that's the easiest/quickest way to think about it. Don't just think about the possibilities because sometimes one possibility is more likely...

[Chseeads]

I'm still trying to figure out if Robert was on the eastbound or westbound train, and exactly how fast his train was going......

[MelodyB]

...and did it leave from New York or Chicago?

[Sis]

Leave it to Nic the math whiz. It's her area of expertise, so I'd believe what she says.

I knew what you meant, but not sure how to go about figuring it out.

[newkris]

perfect.  thanks guys. 

i knew someone (nic) would know what i meant and how my brain works. 

thanks, CD, too. 

it makes sense now, i think. 

and, yep, it's autosomnal recessive. 

the grandmother's generation is important because it means that the mother could be a carrier - even though she isn't affected.  it's an unknown, but we have to assume she is if someone in her generation, or history, is affected.  in this case, her sister is affected so we know the gene exists in that line of the family.

since this is a rare disease, we have to assume that anyone marrying into the family is not a carrier.  that's why they are A_. 

as for the train, it was NOT headed to moscow that's for sure. 

THANKS GUYS!!

[nicolejoy]

Does the question say whether or not the mother is a carrier? Or just that she may be a carrier and that she has a sister who is affected? If that's the case then the answer would be slightly different...

The MOTHER would have a 2/3 chance of being a carrier and a 1/3 chance of being unaffected (I know I said it had to be out of four, but we already know that she doesn't have the disease so we can rule out the aa possibility leaving 3 other possibilities)

I just realised I read your question wrong as well and I was just talking about if both parents were carriers.

In this situation though, if we don't know whether or not the mother is a carrier, you need to work out the probabilities for both situations.

If the mother and father are both NOT carriers, then the child definitely won't be a carrier either. (probability = 0)
If the mother IS a carrier and the father is not a carrier, there's a 2/4 (1/2) chance of the child being a carrier and a 2/4 (1/2) chance of her not being a carrier.

Now you would multiply the probabilities together - if the mother is not a carrier is 1/3, multiplied by 0 is 0, and add it with if the mother IS a carrier, then it's 2/3 multiplied by 1/2, that's 1/3.

That's if the question says that the mother MAY be a carrier but doesn't specifically say if she is or not...

Sorry, my first answer was a bit too simple - but hopefully the graph and the table help - that helps me to think about it the right way and not get confused...

[nicolejoy]

Oh I'm so dumb!! There's Mary AND Robert - I was thinking they were the same person. So my first answer is right for Robert, and my 2nd answer is Mary's kind of situation. Teaches me to read the question properly

[newkris]

so, nic, am i multiplying this right for mary? 

her great-grandmother must be a carrier for her grandmother's sister to be aa so the grandmother is assumed to be Aa.  she marries a man who is assumed to be AA (because it's rare and so it's assumed to be non-existent, although not proven). 

so that means that mary's mother (unaffected) is A_ (we don't know if she's a carrier or not, but have to assume she could be).  mary's mother would then be 2/3, right? 

mary's mother marries a man who is assumed to be AA (because it's rare and assumed).  so then mary is also 2/3, right?

or do i multiply up the generation ladder so that makes Mary 4/9 probability of being a carrier?  (2/3 for her mother, 2/3 for her grandmother multiplied by each other)

OR is mary 2/3 and then i multipy that by robert's probability which i believe is also 2/3 making their babie's chance 4/9? 

we don't know for sure without blood work so we're assuming the probablity based only on family history.

[nicolejoy]

Mary's grandparents MUST be carriers for her aunt to be aa. So her mother MAY or MAY NOT be a carrier. But we know that she's NOT affected. So Mary's mother's chance of being a carrier is 2/3

For Mary, if we KNOW that she's unaffected, then you're right her chance of being a carrier is 2/3 times 2/3 = 4/9

BUT if we're speaking theoretically before she's born, then we need to also consider the possibility that she may have the disease as well, so instead we use my previous post explanation and it's 2/3 times 1/2 = 1/3.

So is Robert the dad? And Mary and Robert are getting married??

If they were SMART they'd get blood work

[newkris]

they did, albeit a  bit late as mary was already pregnant so they tested themselves and their unborn child.

the argose gel shows the child is not affected and not a carrier.  (for which the creationist in the class are thankful to God and the evolutionist are thankful, but they don't know to who.  )


now i'm at the part of the test where they are considering preimplantation genetic testing for future pregnancies.  what do you think of that option for mary and robert?

[newkris]

and yes, robert and mary are married.  this is, after all, a catholic college. . . .