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

The colour of your eyes is caused by pigment molecules in the iris, the ring that surrounds the black pupil in the centre.

While eye colour is actually more complicated than the this, dark eyes (such as brown or black) is dominant (E) and light eyes (such as blue or grey) is recessive (e).

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A father and a mother both have brown eyes. Their two sons have blue eyes and their two daughters have brown eyes. One daughter carries the gene for blue eyes, the other doesn't.

homozygous dominant male

heterozygous/carrier male

homozygous recessive male

homozygous dominant female

heterozygous/carrier female

homozygous recessive female

homozygous dominant genotype

heterozygous/carrier genotype

homozygous recessesive genotype


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


  2. Is the mother homozygous or heterozygous?


  3. What percent of the children are homozygous recessives?


  4. If one son gets married and all his children have brown eyes, what must the genotype of his wife be?


  5. How could the cross for the parents (father x mother) be written using the "dash" technique for unknown genes?


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© Copyright 2008, E. Kimmel