Question

In humans, one type of malignant eye tumor called retinoblastoma is inherited as a dominant allele R. The normal allele r is recessive. what is the probability of the parents in the following crosses having a child with retinoblastoma? draw out each nunnery square and clearly state the requested probability;

heterozygous parent x normal parent

heterozygous parent x heterozygous parent

Answer 1

The retinoblastoma gene is a gene that is involved in stopping cells from crossing the G1 checkpoint in the cell cycle, preventing cells from entering S phase and replicating their DNA in preparation for cell division. For the retinoblastoma gene to be rendered in active,it needs a mutation in both of its copies( allelles). Retinoblastoma is caused by a genetic disorder that usually affects children, impacting their retina's nerve cells, causing them to mutate. This genetic mutation, causes the nerve cells to multiply, and grow, eventually overcoming healthy cells. The rapid growth of the mutated cells can ultimately form and tumor behind the eye.

The tumur syndrome appears in two forms

1. Unilateral retinoblastoma - some children, those who are born into families with no history of retinoblastoma, present with a single tumor in one eye or the other. I this tumor is eliminated, either by radiation or by removal of the affected eye, then this child has no further risk of retinoblastoma and no risk of tumors elsewhere in the body. This is a sporadic form of this disease. Since this form of the disease affects only a single eye, its is often termed unilateral retinoblastoma.

2. Bilateral retinoblastoma - The familial form of retinoblastoma appears in children having a parent who also suffered from the disease, there are ususally multiple foci of tumor arising in both eyes. Curing the eye tumors does not protect these children from a greatly increased risk of other cancers. Those who survive these tumors, in half of their offspring, the famillial form of retinoblastoma again rears its head.