In humans, a form of anmia called thalassemia shows incomplete dominance; hetero
ID: 78011 • Letter: I
Question
In humans, a form of anmia called thalassemia shows incomplete dominance; heterozygotes (Tt) exhibit a mild form of the disease (thalassemia minor) and homozygotes (TT) show a much more severe form (thalassemia major). Homozygous recessive individuals (tt) show no symptoms of anemia. The inheritiance of the ABO blood groups is govenre dby a series of mulitple alleles, where I^A and i^B are codominant and i is recessive to both. A man with thalassemia minor and blood type AB and a woman with no symptoms of anemia and blood type AB have children. What is the probability that they will have.....a) a child with thalassemia minor and blood type B? ...b) two sons with thalasemmia minor with blood type A?
Explanation / Answer
Parents Thalassemia minor, AB x No symptoms, AB
Genotype Tt IAIB ttIAIB
Gametes TIA, TIB, tIA, tIB tIA, tIB
Progeny
TtIAIA
Thalassemia minor, A group
TtIAIB
Thalassemia minor, AB group
ttIAIA
Normal, A group
ttIAIB
Normal, AB group
TtIAIB
Thalassemia minor, AB group
TtIBIB
Thalassemia minor, B group
ttIAIB
Normal, AB group
ttIBIB
Normal, B group
a) Here we see all the possible combinations in the progeny. Out of 8 possible combinations, only 1 combination (TtIBIB) will result in thalassemia minor child with blood group B. So, the probability is 1/8.
b) The probability of a child with thalassemia minor child with blood group A (TtIAIA) is 1 in 8 (as per the table shown above). Now the child can be male or female. So, the probability of the child being male is 1/2 (equal chances of being male or female). Hence the chances of getting one son with thalassemia minor and blood group A is 1/8 X 1/2= 1/16. Chances of having two sons with thalassemia minor and blood group A is 1/16 x 1/16= 1/256.
Gametes TIA TIB tIA tIB tIATtIAIA
Thalassemia minor, A group
TtIAIB
Thalassemia minor, AB group
ttIAIA
Normal, A group
ttIAIB
Normal, AB group
tIBTtIAIB
Thalassemia minor, AB group
TtIBIB
Thalassemia minor, B group
ttIAIB
Normal, AB group
ttIBIB
Normal, B group