Codominance, Incomplete Dominance, Blood Groups

Genetic Problem Set #2:

Codominance, Incomplete Dominance, Blood Groups

1)In cattle, the alleles for red coat (R) and white coat (W) behave as the co-dominants. Both red and white hairs are produced in the heterozygote producing a coat pattern that is called "roan."

A) Give the phenotypic and genotypic ratios to be expected among the offspring from a cross of two roan animals.

B)What are the expected genotypic and phenotypic ratios from a cross of a roan animal and a white one?

2) In some plants, a true-breeding, red-flowered strain gives all pink flowers when crossed with a white-flowered strain: RR (red) x rr (white)  Rr (pink). Stem height is inherited as it is in pea plants (tall (T) is dominant to short (t)). What will be the genotype and phenotype ratios of the generation resulting from the following crosses:

A) Tall-Red (true-breeding) x Short-White?

B) The F2 generation of the cross described in part A?

3) Color pattern in a species of duck is determined by one gene with three alleles. Alleles H and I are codominant, and allele i is recessive to both. How many phenotypes are possible in a flock of ducks that contains all the possible combinations of these three alleles? (HINT: write out all possible genotypes first, then the phenotypes)

4) In humans type A blood is caused by the antigen A in the red cells resulting from gene A. Type B is caused by a gene B for antigen B. Type O blood results from the absence of either gene while the presence of both genes causes both antigens to be formed resulting in type AB blood. If a person of blood group AB marries one belonging to blood group O what will be the blood groups of their children? Show the Punnett square for this cross.

5) If one parent has type A blood and the other has type B, but all four types are represented among the offspring, what are the genotypes of the parents? Show the Punnett square

6) If both parents are type A but half of their children are type A and half of the children are type O, what are the parent's genotypes?

7) In a case of disputed paternity, the mother belongs to group B, the child to O, one possible father to A and the other to AB. Which one is the true father of the child?

8) Mrs. Doe and Mrs. Roe had babies at the same hospital at the same time. Mrs. Doe took home a girl and Mrs. Roe a boy. Mrs. Roe was sure that she had had a girl and brought suit against the hospital. Blood tests showed that Mr. Roe was type O, Mrs. Roe was type AB, Mr. and Mrs. Doe were both type B. The baby girl was type A and the boy was type O. Had an exchange in the babies occurred? How do you know?

9) What are the possible blood types of children in the following families?

A) Type A mother, Type A father

B) Type A mother, TypeAB father

C) Type AB mother, TypeAB father

D) Type A mother, Type B father

10) Imagine that a newly discovered, recessively inherited disease is expressed only in individuals with type O blood, although the disease and blood group are independently inherited. A normal man with type A blood and a normal woman with type B blood have already had one child with the disease. The woman is now pregnant for a second time. What is the probability that the second child will also have the disease? Assume both parents are heterozygous for the “disease” gene.

11) In mice, black color (B) is dominant to white (b). At a different locus, a dominant allele (A) produces a band of yellow just below the tip of each hair in mice with black fur. This gives a frosted appearance known as agouti. Expression of the recessive allele (a) results in a solid coat color. If mice that are heterozygous at both loci are crossed, what will be the expected phenotypic ratio of their offspring?

12)The Case of the Suspected Father:

Blood typing is often used as evidence in paternity cases in courts, but it cannot be used to convict a man, only exonerate him (show that he is not the father!). In a series of disputed paternity cases, the mother and child each had the blood types listed in the table below. For each, indicate the blood types (phenotypes!) which, if found, would exonerate (free) an accused man.