Question

Researchers estimate that 1/3 of all retinoblastoma cases are hereditary, while the other 2/3 are sporadic (non-hereditary). It develops in early childhood. A couple has one child with bilateral retinoblastoma. The mother has no history of cancer, but the father had bilateral retinoblastoma as a child.  

1. Explain the molecular basis of cancers that get inherited in families

2. Why are familial cases frequently bilateral (occurring in both eyes), while nonspecific cases are unilateral (occurring in one eye)?

3. What are the odds or chances the second child will have this?

4. What is meant by the sentence: Cancer susceptibility is inherited in a dominant fashion, but the phenotype is recessive at a cellular level

Answer 1

1.Uncontrolled growth of cells is termed as cancer.It is caused by an abnormal change in a gene(ie ;mutation).Gene mutations can be either inherited or acquired.Let us consider the inherited gene mutation.An inherited gene mutation is present in the egg or sperm cell of the newborn child. When the egg is fertilized by the sperm, it creates one cell that then divides many times and eventually becomes a baby. Since all the cells come from this first cell, this kind of mutation is in every cell (including eggs or sperm) and so can be passed on to the next generation.This is the molecular concept of cancer passing to the next generation (tumor suppressor genes).

2.Retinoblastoma can be hereditary or nonhereditary.A bilateral Retinoblastoma is caused by the presence of multiple tumors in the affected eye,this multiple tumors caused by the repeated mitotic division that took place to the formation of blastocyst at the time of birth.

3.If gennetically the first child inherited Retinoblastoma then the chances of being affecting the second child is 50%.Otherwise it would be less than 5%.

4.This is clear from the case of Retinoblastoma. A dominant case is known here as bilateral case of Retinoblastoma and recessive case known as lateral Retinoblastoma.

For example if AA for bilateral case of Retinoblastoma,then the lateral case of Retinoblastoma is aa.