EK Bio Lecture 2 Exam Q.44

[jjunior]

Hi, can someone explain this question to me? i dont even know where to start with this one

here is the question:
Turner's syndrome occurs due to nondisjunction at the sex chromosome resulting in an individual with one X and no Y chromosome. Color-blindness is a sex-linked recessive trait. A-color-blind man marries a healthy woman. They have two children both with Turner's syn- drome. One of the children is color-blind. Which of the following is true?
A. Nondisjunction occurred in the father for both children.
B. Nondisjunction occurred in the mother for both children.
C. Nondisjunction occurred in the mother for the color-blind child and in the father for the child with normal vision.
D. Nondisjunction occurred in the father for the color- blind child and in the mother for the child with nor- mal vision.

the answer states:
C is correct. Both children are female, because the genotype of Turner's syndrome, as per the question, must be XO. The 0 came from the parent within whom nondisjunction occurred; the X came from the other parent. The mom only has healthy Xs to pass on, the father has only one colorblind X to pass on. Thus the colorblind child got her X from Dad and her 0 from Mom, and the healthy child got her X from Mom and her 0 from Dad.

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[sazerac]

Hi, can someone explain this question to me? i dont even know where to start with this one

here is the question:
Turner's syndrome occurs due to nondisjunction at the sex chromosome resulting in an individual with one X and no Y chromosome. Color-blindness is a sex-linked recessive trait. A-color-blind man marries a healthy woman. They have two children both with Turner's syn- drome. One of the children is color-blind. Which of the following is true?
A. Nondisjunction occurred in the father for both children.
B. Nondisjunction occurred in the mother for both children.
C. Nondisjunction occurred in the mother for the color-blind child and in the father for the child with normal vision.
D. Nondisjunction occurred in the father for the color- blind child and in the mother for the child with nor- mal vision.

the answer states:
C is correct. Both children are female, because the genotype of Turner's syndrome, as per the question, must be XO. The 0 came from the parent within whom nondisjunction occurred; the X came from the other parent. The mom only has healthy Xs to pass on, the father has only one colorblind X to pass on. Thus the colorblind child got her X from Dad and her 0 from Mom, and the healthy child got her X from Mom and her 0 from Dad.

Healthy mom: XX
Healthy dad: XY
Healthy child: gets one letter from each parent

This mom: XX
This dad: xY (notice the small x, because he has an X-linked disease of color blindness)

Non-disjunction: get more or less than one letter form each parent
Turners: a non-disjunction where you only get one X (from mom or from dad)

Child 1: only X
Child 2: only x (notice the small x because this child has the color blind disease)

Who did child 1 get the capital X from?
Which parent forgot to donate a letter?

Who did child 2 get the small x from?
Which parent forgot to donate a letter?