Pedigrees for several individuals

Question

The pedigree below shows the parents and siblings of the married couple Tom and Mary. Note that Tom (E? - brown eyes) and Mary (ee - blue eyes) have one child that shows the recessive trait of blue eyes (ee). (Remember the shaded in shapes are affected individuals.)

Long Description of above pedigree: A genetic pedigree diagram for an autosomal trait. Tom (open square) does not show the recessive trait because he has brown eyes but his wife, Mary, does show the autosomal recessive trait (blue eyes). One of their male children exhibits the recessive trait (ee).

1. What are the genotypes of the following individuals in the pedigree.

a. Tom

b. Mary

c. Mary’s mother

2. Tom and Mary are expecting their second child. What are the chances that their child will have blue eyes? (Show all work, i.e. Punnett Square.)

Part III: Non-Mendelian Genetics

1. In four-o’clock flowers red petals are incompletely dominant over white petals, producing pink petal flowers in the heterozygous stage. What would be the probability of having white offspring if two pink flowered plants were crossed?

2. In humans, there are three alleles for blood types, A = IA, B = IB, and O = i. Type A and B are co-dominant alleles and type O is recessive. Could a man with type AB blood be the father of a child with type O blood if the mother was heterozygous for type A blood?

Answer 1

Part I (the pedigree)

1) Tom has to have the genotype Ee because he has brown eyes, so he must have one E, but he passes on the blue-eyed trait to his son, so the second allele must be e. If Tom was EE, then he could not have a blue-eyed son.

2) Mary has to have the genotype ee because she has blue eyes and that is recessive, so she has to have two recessive alleles.

3) Mary's mother had to have at least one e allele because she passed that on to Mary. However, in order to know whether Mary's mother was Ee or ee, we would have to know if she had brown or blue eyes or know information about her parents.

4) If Tom is Ee and Mary is ee, they have a 50% chance of having a child with blue eyes.

Part II: the flowers

1) A pink flower has a red allele and a white allele, making the genotype RW or C^R C^W, depending on the notation style your teacher uses. If two pink flowers are crossed, there is a 25% probability of getting a white-flowered offspring.

Part III: blood types

1) Someone with type O blood would have the genotype ii. Someone with type AB blood has the genotype I^A I^B, which means this person could only pass on an A allele or a B allele. They do not have an O allele (i) to pass on to a child, so it is impossible for them to have a type O child regardless of the mother's blood type.