Question

Describe a trait/disease for codominant inheritance in blood type and use a Punnett square to demonstrate the inheritance of the trait/disease (include phenotypic ratios, genotype ratio, genotype of parents and phenotype of parents) Show your key.

Answer 1

Describing the codominant inheritence of Hemophilia:

Let's have a glance at a depiction of Punnett square using hemophilia ( X-linked human disorder), which is generally a recessive disorder in which an affected patient's blood does not clot properly. A patient having hemophilia may have to suffer from even life-threatening, bleeding from just even a small cut.

Hemophilia occurs due to the mutation in either of two genes, both of which are located on the X chromosome. Both genes encode proteins that help blood clot. Let's focus on just one of these genes, calling the functional allele X^H and the disease allele X^h

In our example, a woman who is heterozygous for normal and hemophilia alleles X^H X^h has children with a man who is hemizygous for the normal form (X^HY). Both parents have normal blood clotting, but the mother is a carrier. What is the chance of their sons and daughters having hemophilia?

Since the mother is a carrier, she will pass on the hemophilia allele X^h on to half of her children, both boys and girls.

• None of the daughters will have hemophilia (zero chance of the disorder). That's because, in order to have the disorder, they must get an X^h allele from both their mother and their father. There is 0 chance of the daughters getting an X^h allele from their father, so their overall chance of having hemophilia is zero.

• The sons get a Y from their father instead of an X, so their only copy of the blood clotting gene comes from their mother. The mother is heterozygous, so half of the sons, on average, will get an X^h allele and have hemophilia (1/2 chance of the disorder).