PATHOLOGY

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PATHOLOGY MCQ

GENETICS AND DISEASE

Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
A common form of muscular dystrophy is an X-linked disorder that causes progressive weakening of skeletal muscles. It is usually passed from a mother to a son. A mother who is a carrier for this disorder (XX’) marries a man who is normal (XY). Which of the following is a true statement about the couple’s sons? You will need to work a Punnett square to figure it out. (3B3)
A
There is a 25% chance that each son will have the disorder
B
There is a 50% chance that each son will have the disorder
C
There is a 75% chance that each son will have the disorder
D
All sons will be born with the disorder
Explanation: 

Detailed explanation-1: -A woman who is a carrier of an X-linked recessive disorder has a 25% chance of having an unaffected son, a 25% chance of having an affected son, a 25% chance of having an unaffected daughter and a 25% chance of having a daughter who also is a carrier.

Detailed explanation-2: -However, all daughters of a man with hemophilia are considered obligate carriers of hemophilia because they must receive the affected X chromosome from their fathers to be female, and they can pass the gene to their sons.

Detailed explanation-3: -Which of the following would be true of all daughters born to a man with hemophilia, regardless of who the mother is?-All daughters would carry at least one gene for hemophilia but would not necessarily have the disorder.

Detailed explanation-4: -Red-green color blindness is more prevalent in men since it is inherited via the X chromosome. This is due to the fact that males inherit just one X chromosome from their mother. They will suffer red-green color blindness if that X chromosome carries the red-green color blindness gene rather than a normal X chromosome.

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