Many types of color blindness are what are called X linked, thatis determined by

Question

Many types of color blindness are what are called X linked, thatis determined by genes on the X chromosome. Suppose a woman iscarrying one X chromosome with the gene for a particular type ofcolor blindness; her other X chromosome does not have this gene. Ifshe is married to a man who does not have this gene on his Xchromosome. You may remember that color blindness is X linkedrecessive.

A. What is the probability that her first child will carry the Xchromosome with the gene associated with color blindness?

B. Suppose amniocentesis reveals that the child is male.What is the probability that the child is color blind. Hint: thisinvolves conditional probability

Explanation / Answer

Color blindness - X linkedTRAIT                       

                 NORMAL FATHER         XY                  CARRIERMOTHER   XXC

GAMETES

X

XXC

X

XX NORMAL

XXC   CARRIER

Y

XY NORMAL

YXC       AFFECTED

                        50%

B. Suppose amniocentesis reveals that the child is male. What isthe probability that the child is color blind.

             50%

GAMETES

X

XXC

X

XX NORMAL

XXC   CARRIER

Y

XY NORMAL

YXC       AFFECTED

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