Answer:
0
Explanation:
This is a cross involving a single gene coding for tongue rolling in humans. The allele for tongue rolling (T) is dominant over the allele responsible for inability to roll the tongue (t).
Thus, a homozygous recessive individual will have a tt genotype and be phenotypically unable to roll his/her tongue. If two homozygous recessive individuals (tt) are crossed, all the offsprings will have a homozygous recessive (tt) genotype and be unable to roll their tongues.
Hence, the chance of two homozygous recessive individuals producing an offspring that can roll his/her tongue is zero (0) because it cannot occur.