Biology dat destroyer help!!

[RING12]

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on q.128 says: a normal woman had a colorblind mother. she marries a colorblind man. What is the porbablility that her first daughter will be colorblind?


the answer doesnt make any sense. It says 50% but I got 25%. and even on the solution says 50% of the sons are colorblind as well, which is wrong.

Can some one explain this to me please!!!

 

[MAdental]

prob of having a daughter is 1/2. colour-blindness is a recessive trait and is sex linked ( men usually) but the the question says she had a colour-blind mom (women have it too ?) so we go with that. If she is normal BUT had a color blind mom then she is X^B X^b. the dude is colour-blind so he definitely passes the gene since the child is a girl.( X^b passed on)

1/2 chance of getting a daughter x 1/2 chance of having a color-blind daughter= 25%, destroyer is wrong. is it 2011 version?

EDIT: question says if her first daughter.....so you already know its a girl. so its 1 x1/2 =1/2

If it had said if the child was a daughter and was colour-blind, then you 25%.

 

[woox]

ignore the sons in question...poorly worded question

 

[FROGGBUSTER]

This one's a little tough.

Let c = colorblindness, c+ = normal. Note: the color-blind gene resides on the X chromosome.

The woman's mother was cc, so if the woman is normal, she has to be cc+.

She marries a man who is c+Y.

Since the question specifically asks about the probability of a daughter having colorblindness, we know the man HAS to donate c+. If it were asking about a boy, he would donate his Y chromosome instead.

The woman has a 50% chance of donating c and a 50% chance of donating c+.

This means there is a 50% chance the daughter is cc+ (normal) and a 50% chance the daughter is cc (color-blind).

 

[FROGGBUSTER]

prob of having a daughter is 1/2. colour-blindness is a recessive trait and is sex linked ( men usually) but the the question says she had a colour-blind mom (women have it too ?) so we go with that. If she is normal BUT had a color blind mom then she is X^B X^b. the dude is colour-blind so he definitely passes the gene since the child is a girl.( X^b passed on)

1/2 chance of getting a daughter x 1/2 chance of having a color-blind daughter= 25%, destroyer is wrong. is it 2011 version?

If the question states that the couple have a daughter, the probability they have a daughter is just 1 already, lol. So you would multiply 1*1/2 = 1/2 as your answer.

 

[MAdental]

But 50% of sons cant be color-blind cuz the dad passes the Y only and Y doenst have any trait genes on it!!!!!!!!

 

[FROGGBUSTER]

But 50% of sons cant be color-blind cuz the dad passes the Y only and Y doenst have any trait genes on it!!!!!!!!

Maybe I'm missing something, but I would agree with 50% of sons are color blind.

Dad contributes Y, while Mom contributes either c (colorblind) or c+ (normal).

Thus, 50% of sons are cY while 50% of sons are c+Y.

 

[MAdental]

Maybe I'm missing something, but I would agree with 50% of sons are color blind.

Dad contributes Y, while Mom contributes either c (colorblind) or c+ (normal).

Thus, 50% of sons are cY while 50% of sons are c+Y.

ya you are right. It is sex linked and it only exists on a X chromosome. so 50% chances of mom giving it or not giving it. I confused it with PKU which is autosomal recessive.

 

[RING12]

My problem is I look at it as 1/4 carrier and 1/4 healty. so it's gonna be 25 % not 50%. same for men. 1/4 is health and 1/4 is is sick. maybe for this type problem I shouldnt look it this way just I should look 50% healthy and 50% sick. Im confused!!!

 

[FROGGBUSTER]

My problem is I look at it as 1/4 carrier and 1/4 healty. so it's gonna be 25 % not 50%. same for men. 1/4 is health and 1/4 is is sick. maybe for this type problem I shouldnt look it this way just I should look 50% healthy and 50% sick. Im confused!!!

Yeah always just look at it either as normal or afflicted for genetics problems (unless they ask you specifically for carriers).

 

[RING12]

Yeah always just look at it either as normal or afflicted for genetics problems (unless they ask you specifically for carriers).

guess what! I just found out the answer is wrong. Q147. is similar problem but the answer is 25%. so Im guessing I was right. the answer to 128Q was wrong. it should be 25% not 50%.

 

[FROGGBUSTER]

guess what! I just found out the answer is wrong. Q147. is similar problem but the answer is 25%. so Im guessing I was right. the answer to 128Q was wrong. it should be 25% not 50%.

Which edition of Destroyer do you have? I have the 2011 version and it is question 148 for me. The answer says 50%.

I know Destroyer has mistakes, but I am almost 100% positive the answer is 50%. I took a Genetics course last semester and we did these all day long, so I was pretty certain in my methodology.

 

[RING12]

Which edition of Destroyer do you have? I have the 2011 version and it is question 148 for me. The answer says 50%.

I know Destroyer has mistakes, but I am almost 100% positive the answer is 50%. I took a Genetics course last semester and we did these all day long, so I was pretty certain in my methodology.

oops,Im sorry. I ment 147. but I saw 148 and then I got confused again. I dont understand 127,147 and 148 should have different answers??? 🙁

 

[FROGGBUSTER]

oops,Im sorry. I ment 147. but I saw 148 and then I got confused again. I dont understand 127,147 and 148 should have different answers??? 🙁

Are you sure you have the 2011 version? My 127 is another question entirely.

 

[FROGGBUSTER]

If the question states that the couple have a daughter, the probability they have a daughter is just 1 already, lol. So you would multiply 1*1/2 = 1/2 as your answer.

I posted this above.

Read that and maybe it will help. I think you're taking into account the probability they birth a daughter over a son; you shouldn't because it already says daughter in the problem.

 

[RING12]

I posted this above.

Read that and maybe it will help. I think you're taking into account the probability they birth a daughter over a son; you shouldn't because it already says daughter in the problem.

I have 2010 version.

 

[RING12]

I posted this above.

Read that and maybe it will help. I think you're taking into account the probability they birth a daughter over a son; you shouldn't because it already says daughter in the problem.

I have 2010 version.

 

[rah08e]

I't seems like everyone is over thinking this question. The question tries to trick you by asking the probability that her first daughter will be color blind. Since they only ask about the daughter's traits, you only look at the daughters traits. After the test cross, 1 daughter will express, 1 daughter will carry, 1 son will express, and 1 son will not carry. Looking at just the daughters, only 1 of the 2 will be colorblind....aka 50%

PS.- 50% of the sons are color bind as well.

 

[Locdawgg]

I't seems like everyone is over thinking this question. The question tries to trick you by asking the probability that her first daughter will be color blind. Since they only ask about the daughter's traits, you only look at the daughters traits. After the test cross, 1 daughter will express, 1 daughter will carry, 1 son will express, and 1 son will not carry. Looking at just the daughters, only 1 of the 2 will be colorblind....aka 50%

PS.- 50% of the sons are color bind as well.

Thank you! Just came across this question in the destroyer book. Makes sense now.

 

[hope_to_match]

I't seems like everyone is over thinking this question. The question tries to trick you by asking the probability that her first daughter will be color blind. Since they only ask about the daughter's traits, you only look at the daughters traits. After the test cross, 1 daughter will express, 1 daughter will carry, 1 son will express, and 1 son will not carry. Looking at just the daughters, only 1 of the 2 will be colorblind....aka 50%

PS.- 50% of the sons are color bind as well.

yup very good explanation here. if you do a test cross you will see that 1 daughter will carry and one will EXPRESS the trait because she will get the gene from mother and father. as for the sons- 1 son will express (because only has one x and therefore is bound to get it) and one son won't have it because the other X on mother does not have the trait!

So...they are asking what is the probability of the first daughter expressing? it is 50% because you can't predict which daughter will be born first (i.e. the one who has both alleles or just one)