Question

a. Two women give birth on the same day at the same hospital, and upon leaving are convinced that they have been given the wrong infants. If couple 1 (both type A) gets a child with type A, and couple 2 (type AB and O) gets a child with type O, are their fears reasonable? Why?

b. Colorblindness is a recessive, sex-linked trait. The son of a colorblind man and a woman with normal vision wants to join the air force, but they will not accept applicants who are even slightly colorblind. Should he be concerned that he might have inherited his father’s colorblindness? ____________

Answer 1

a.) Yes, their fears are reasonable. In blood groups one simple sure thing is that , if both parents are "Type O" all their children will be "Type O". But, for other blood types there will be other possibilities.

Usual blood types of prents and their possible infants:

PARENTS BLOOD TYPE	POSSIBLE INFANTS	NOT POSSIBLE INFANTS
A and A	A, O	B, AB
A and B	A, B, AB, O	NONE
A and AB	A, B, AB	O
A and O	A, O	B, AB
B and B	B, O	A, AB
B and AB	A, B, AB	O
B and O	B, O	A, AB
AB and AB	A, B, AB	O
AB and O	A, B	AB, O
O and O	O	A, B, AB

According to blood grouping,

• The couple 1 both with "Type A" blood group could only get the possible infants with "Type A and O". So the 1st couples child is "Type O".
• The couple 2 with "Type AB and O" blood groups could only get the possible infants with "Type A and B". The 2nd couples child is "Type A".
• So the infants were changed in between the couples and their fear was reasonable.

b.) Color blindness is a common hereditary condition which is inherited from parents. But, in this case there is no possibility of getting the son affected with color blindness.

Reasons:

color blind father(XY) normal vision mother(XX)  

no color blind sons(XY) 100% color blind gene carrier daughters(XX).

• The faulty gene for color blindness is found only on X-chromosome. So , for a male to be color blind, the faulty color blindness gene only has to appear on his X-chromosome.
• A color blind boy cannot receive a color blind gene from his father even if his father is color blind because his father can only pass an X-chromosome to his daughters.
• So , in this case there is no possibility of the son getting inherited with color blindness.