Destroyer BIO qes 100

[zvm77]

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"Bill and Ann have normal vision but their fathers are both colorblind. What's the probability that their first child will be a normal boy?"
Ans: 25%

My qes is if you do the punnet square you see that 50% of boys are normal and 50% colorblind. In the and he said 1/2 are color blind and 1/2 not so do 1/2 * 1/2 = 25% my qes is why do you multiply 1/2 * 1/2 why is the ans not just 50%?

 

[jntruong2003]

hey zvm77, its 1/2 * 1/2 because it is 1/2 chance of getting a boy and then 1/2 chance that boy will be colorblind. so 1/2 * 1/2 = 1/4.

 

[gomawum]

I don't get it, since it already stated the 'boy' isn't it just 1/2?
I think other question was similar but it worked this way

 

[jntruong2003]

okay, so colorblindness is a sex-linked trait and is passed by the female who is a carrier to her sons. the genotype of the male is unimportant because males cannot pass the sexlinked trait to males, which is found on the X chromosome. in the punnet square, there will be 1 male with no colorblindness and 1 male who is normal. but you have to remember that the chance to get a male baby is 1/2 chance. of that 1/2 chance of getting a male baby, there is a 1/2 chance of getting colorblindness. therefore, it would be 1/2 * 1/2 = 1/4.

 

[zvm77]

the next qes which deals with hemophilia which is also sex linked asks the same qes about what's the probability of getting a boy with hemophilia and they don't do 1/2 * 1/2 they juts leave it as 1/2 (50%) what's the reason for this I don't see any dif in the 2 qes ?

 

[shvora]

"Bill and Ann have normal vision but their fathers are both colorblind. What's the probability that their first child will be a normal boy?"
Ans: 25%

My qes is if you do the punnet square you see that 50% of boys are normal and 50% colorblind. In the and he said 1/2 are color blind and 1/2 not so do 1/2 * 1/2 = 25% my qes is why do you multiply 1/2 * 1/2 why is the ans not just 50%?

Let's see if I can help you:
1) Bill's father (XcY)is color blind but bill is not so Bill's genotype is XY
2) Ann's father (XcY) is c blind too but she is XcX
3) probability that the first child will be normal =1/2
4) So the probability that the first child will be a boy=1/2
5) now probability that the first child will be boy AND color blind=1/2*1/2=25%


For the hemophilia question pls state the question to determine the parents (Bill and Ann) genotype.

 

[zvm77]

"a woman who is seemingly normal marries a normal man. The woman's father is a hemophiliac, what's the probability the couple's son will have hemophilia?
You get the same results as the baove qes doing the punnet square but leave it as 50% the and, even thoug it also asks about getting the sex linked disease and being a boy, why is getting dif results than the other qes, you should also than do 1/2 chance (for being a boy) * 1/2 chance (hemophilia) = 25%, but the books states that 50% is the ans you don't multiply the 2, why?

 

[jntruong2003]

hey zvm77! the reason why the answer for the 2nd question about hemophilia is 50% is b/c it is ALREADY known that the child is a boy. the question is just asking what the chances are that the boy is a hemophiliac. the boy when he was born had a 50% chance so the answer is 1/2. hope that clarifies things.

 

[joonkimdds]

Take genetics class and this should be the simplest question.

 

[zvm77]

Thanks for our opinion

 

[CannonD]

i agree with Shrova until step 2. So you have XcX=Anna and XY= Bill and when you do square cross you'll get XY, XcY, XcX, XX so the properbility of normal boy is 1/4=25%. I disagree with Shrova on step 3 because the possibilities for the first child to be normal is 75% not 1/2. Yes the possibility for is 1/2 between boys.

 

[bodiddely]

i agree with Shrova until step 2. So you have XcX=Anna and XY= Bill and when you do square cross you'll get XY, XcY, XcX, XX so the properbility of normal boy is 1/4=25%. I disagree with Shrova on step 3 because the possibilities for the first child to be normal is 75% not 1/2. Yes the possibility for is 1/2 between boys.

I think when Shvora said there's a 50% chance the child will be normal they meant non affected/non carrier