The answer would be: A.50%
A child will get genetic material from both parents, half from the father and half from the mother. This is why the gamete cells (sperm/ovum) are made from meiosis and only have 50% of the original genetic material.
In this case, the parent carries a deletion on one of the two homologous chromosomes. Since the gamete only has one of the chromosomes, half of the gamete of this parent would have the defective chromosome and the other half have a normal chromosome. So, the chance for the child to inherit the defective gene is 50%.
