Problem 1: Tongue Rolling
Tongue Rolling
Problem 2: Eye Colour
Eye Colour
Problem 3: Diabetes
Problem 4: Blood Type
Blood Type

Red blood cells have many types of molecules sticking out of their cell membranes. Some of these are glycoproteins that determine your blood type.

The genes that code for these glycoproteins exhibit something called "co-dominance" where IA and IB are both equally dominant but O is still recessive.

The genotype for blood type A is written as IAIA or IAi (where "i" is recessive). Blood type B is IBIB or IBi and blood type O is ii.

But put IA and IB together and you get another blood type, AB, the co-dominant type, where neither the A or B is recessive to the other.

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A father has blood type A and a mother has blood type AB. They have 3 children, a son with blood type A, another son with blood type AB, and a daughter with blood type B. The daughter then marries a man with blood type O and they have a daughter with type O.

Type A male

Type B male

Type AB male

Type O male

Type A female

Type B female

Type AB female

Type O female

homozygous A genotype

heterozygous A genotype

homozygous B genotype

heterozygous B genotype

codominant AB genotype

homozygous O genotype

unknown A and B genotype


  1. Type the cross for the parents (father x mother) in generation 1.


  2. What blood type can the parents in generation 1 NOT produce?


  3. What is the best way to write the genotype of the son with type A blood in generation 2?


  4. What other blood type can be produced in generation 3?


  5. Could the husband of the daughter in generation 2 have blood type B and still produce a type O child?


Pedigree Quiz
© Copyright 2008, E. Kimmel