Retinoblastoma (a rare cancer of the retina) is inherited as an autosomal domina

Question

Retinoblastoma (a rare cancer of the retina) is inherited as an autosomal dominant trait. A heterozygous woman was successfully treated for this disease. If she has a normal husband what percent of her children may be affected with retinoblastoma? Blood types are a Codominant trait, where both alleles are expressed and none are masked. A father comes in to the hospital crying that his son can't be related to him because he has a Blood type of A and his wife has a blood type of B, but their child has a blood type of O. You know that he has nothing to fear, it is possible that the son is indeed his and that his wife did not cheat on him. Explain to him how this is possible.

Explanation / Answer

A)

Genotype of female: Rr

Genotype of male: rr

Rr = 2 / 4 = 50 % (with retinoblastoma)

Rr = 2 / 4 = 50 % (without retinoblastoma)

r

r

R

Rr

Rr

r

rr

rr

B)

Human blood types are encoded by a single locus with three alleles: IAIBIO

IAIB code for two different proteins, cell surface antigen A, or antigen B. : IO codes for the lack of that particular protein.

Since we are diploid, we have a blood type, a phenotype, that depends upon the proteins on the surface of our blood cells.

IAIA and IAIO are A, IBIB and IBIO are B, and IOIO are o.

IA and IB are therefore co-dominant with respect to each other, and both are dominant with respect to IO

Genotype of father: IAIO

Genotype of mother: IBIO

IB

IO

IA

IAIB

IAIo

IO

IoIB

IoIo

r

r

R

Rr

Rr

r

rr

rr

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