In humans, the ability to roll the tongue is a dominant trait. The inability to roll the tongue is a recessive trait. If two individuals homozygous recessive for this trait have a child, what is the chance that the child will be able to roll his tongue?

The correct option is (A):

Explanation of the correct option:

1. ​The ability to roll tongue is dominant over inability to do it.
   
2. If the dominant allele is R and the recessive allele is r, therefore the two individuals have the homozygous recessive character.
3. This means the genotype of the organism will be 'rr'.
   
4. If two such individuals are crossed:
   

Parents rr X rr

Gametes r r

Offspring rr​

Results of the cross:

1. ​Based on the genetic cross the genotype of the offspring will be rr which is homozygous recessive.
   
2. This is why, the child will not be able to roll their tongue as they do not have the dominant allele.
3. Therefore, there is 0% chance of children having the tongue rolling character.
   

Final Answer: There is 0% chance that the child will not be able to roll his tongue.