Other patterns of inheritance

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

Explain the difference between codominance and incomplete dominance, and give an example of each one.

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.

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.

In the four o'clock plant, flower colour shows incomplete dominance: RR is red, Rr is pink and rr is white. Cross a pink-flowered plant with a white-flowered one and state the genotypic and phenotypic ratios of the offspring.

In four o'clock plants, flower colour 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.

For the ABO blood groups there are three different alleles, but each person only has two of them. Explain what multiple allelism is and why this happens.

A person with blood group AB and another with heterozygous blood group A ($I^A i$) have a child. Calculate the probability of each possible blood group in the offspring and reason why the child cannot be group O.

In a hospital maternity ward, a mix-up with three newborns occurred following a technical incident. The blood types of the three babies and the three couples have been determined:

• Baby 1: Type 0

• Baby 2: Type AB

• Baby 3: Type B

• Couple X: Both parents are type AB.

• Couple Y: The mother is type A and the father is type B; both know that their respective fathers (the child's grandfathers) were type 0.

• Couple Z: The mother is type 0 and the father is type AB.

1. a) Reasonably assign each baby to their corresponding couple. To do this, deduce the parents' genotypes and explain why you rule out the other combinations.
2. b) If Couple Y decided to have another child, what would be the probability (in percentage) that they are born with the same blood type as Baby 2?

Explain what it means for a gene to be linked to the X chromosome and reason why men (XY) have only one allele for those genes, while women (XX) have two.

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 colour-blind man ($X^d Y$) has children with a woman with normal vision who is not a carrier ($X^D X^D$). State the genotypes and phenotypes of the sons and of the daughters, and explain why this type of inheritance is said to go "criss-cross" from fathers to daughters.

A couple attends a genetic counseling consultation: the man has normal vision and so does the woman, but she is concerned because her maternal grandfather was color-blind (her maternal grandmother and her father had normal vision and had no family history). The man claims there is nothing to worry about, stating: "Since I am not color-blind, it is impossible for us to have a color-blind daughter or son."

1. a) Reasonably deduce the probability that the woman is a carrier based on the data from her maternal family.
2. b) Refute or validate the man's claim using genetic arguments for daughters and sons separately, showing the possible crosses.
3. c) Calculate the final probability that the first child born to this couple is a color-blind male.

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.

A man with hemophilia ($X^h Y$) and a homozygous non-carrier woman ($X^H X^H$) have offspring: a son and a daughter. Upon reaching adulthood, both children have offspring with healthy partners who have no history of the disease.

The son fears transmitting hemophilia to his children, while the daughter is convinced that her offspring can never suffer from it "because her own mother did not carry the disease allele."

1. a) Using the F1 and F2 crosses, evaluate the fears and beliefs of both siblings and determine which of the two is making an error in their reasoning.
2. b) Calculate the probability that a grandson (son of the daughter) will have hemophilia and the probability that a granddaughter (daughter of the daughter) will be hemophilic.
3. c) Explain at a cytogenetic level why this type of sex-linked recessive traits exhibits a pattern of inheritance with phenotypic generation skipping in the male lineage.