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#1




Calculating the probability of two traits in genetics!
How do I do this question?
Colorblindness is a recessive, Xlinked trait. A couple, who are both blood type A and who both have normal vision, have a son who is blood type O and color blind. What is the probability that their next child will be a daughter who is blood type O and has normal vision? A. 1/2 B. 1/4 C. 1/8 D. 1/16 E. Zero  not possible How do I do this problem? I got the answer as 1/4 while the correct answer, according to the book is 1/8. 
#2




1)probability of having a girl is 50%,boy is 50%
2)they are both AO,therefore they have chances of 25% AA child,50% AO and 25% OO chances of a girl with OO is 50% * 25%=1/8
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#3




Since both parents are type A and their first child is type O, you know that both parents are heterozygous for blood type A, meaning that one chromosome they have is A and the other is type O. For a child to be blood type O, each parent has to give their type O chromosome to the child. There is a 1/2 chance that one parent will give the recessive O chromosome, so for both parents to give their recessive allele the probability is 1/2 * 1/2 = 1/4
Colour blindness is an Xlinked condition, that means that women can be carriers but not manifest the colour blindness because they have one "good" X chromosome which masks the recessive colourblindness gene on the other X. The father cannot have a colourblindness gene or else he'd be colourblind himself, since he's only got 1 Xchromosome. Because dad has healthy eyesight, any girls he has will have healthy eyesight too, since his X will always be healthy and mask the X from mom if she happens to give the recessive colourblind gene. So the probability that the girl will have normal vision is 1/1. However, it is not a given that the baby born will be a girl, there's a 50/50 chance that it'll be one or the other sex, so we need to consider the probability involved with the child being a girl. this probability is 1/2. So now we multiply all our probabilities together to calculate what the chances of a normal visioned, type O blood typed girl is: Normal vision (1) * blood type O (1/4) * girl baby (1/2) = 1/8 So your probability is 1/8! 
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