Exercises: Other patterns of inheritance

Explain what codominance is and give a human example in which two alleles are expressed simultaneously.

Explain what incomplete dominance is and describe which phenotype appears when crossing a red-flowered plant with a white-flowered plant if the trait follows this pattern.

The alleles $I^A$, $I^B$ and $i$ are involved in blood groups. State which genotypes correspond to blood groups A, B, AB and O.

A person with blood group AB and a person with blood group O have a child. State the possible blood groups of the child and their probabilities, excluding each parent's blood group from the possibilities.

In four o'clock plants, flower color shows incomplete dominance: red (RR), pink (Rr) and white (rr). Complete the Punnett square in the diagram, where two pink-flowered plants are crossed, and state the genotypic and phenotypic ratios of the offspring.

In humans, sex is determined chromosomally: females are XX and males are XY. Explain, using the corresponding cross, why the probability of having a son or a daughter is equal (1:1 ratio) and which parent provides the chromosome that determines the sex of the offspring.

A woman who is a carrier of the color-blindness allele ($X^D X^d$) has children with a man with normal vision. What is the probability of each son being color-blind? And each daughter? Reason both answers using a genetic cross.

A medical emergency occurs in a hospital and a patient with blood type 0 urgently needs a transfusion. When testing their biological parents, it is found that the father is type A and the mother is type B. A student intern claims that there must be an error in parentage, arguing that "two parents with dominant A and B antigens can never produce a type 0 child, who lacks both antigens."

1. a) Refute the student's statement by deducing the exact genotypes that the parents must have, and represent the cross that demonstrates the genetic viability of the patient's birth.
2. b) If this same couple has more offspring, predict the expected phenotypic percentages for each blood type.
3. c) Justify whether any of the future siblings could donate red blood cells to the type 0 patient.

Queen Victoria of Great Britain was a heterozygous carrier of hemophilia ($X^H X^h$) and her consort, Prince Albert, had normal blood clotting ($X^H Y$). Among their descendant European dynasties, several affected males were observed, but no female with hemophilia.

1. a) A rumor at the time claimed that if Prince Albert had been hemophilic, 100% of the couple's daughters would have been born with the disease. Demonstrate through a genetic cross whether this statement is true or false, indicating the expected phenotypic and genotypic percentages for daughters in that scenario.
2. b) Deduce what two simultaneous genetic and phenotypic conditions had to coincide in both parents for a hemophilic girl to be born in that era.
3. c) Justify at the chromosomal level why males cannot be healthy carriers of an X-linked recessive disease.