Answer: The correct answer is 25%.
As per the question, genetic disorder is caused by recessive allele. This means that that genotype of the person having the recessive disorder is gg.
A dominant allele ( depicted by capital letter like G in this case) always masks the expression of recessive allele.
A recessive disorder will only be caused when the person is homozygous for the recessive allele ( like in this case gg is the genotype that will cause the disease.
In the given question, genotypes of parents is Gg and Gg.
The chances that their children will inherit the disorder is 25%. Refer punnett square.
