Answer: one offspring out of the four will have a recessive-recessive genotype.
Explanation: A cross between two parents who are heterozygous for a gene that has a simple dominant-recessive pattern of inheritance will produce four offsprings: one will be homozygous dominant, two will be heterozygous dominant while one will be homozygous recessive.
Homozygous dominant offspring has two dominant alleles, heterozygous dominant offspring has one dominant allele and one recessive allele while a homozygous recessive offspring has two recessive alleles.
For example, a cross between two parents that are heterozygous (Tt) for tall will produce one TT, two Tt and one tt. TT is homozygous dominant, Tt is heterozygous dominant and tt is homozygous recessive. An offspring with genotype tt has a two recessive alleles thus have a recessive-recessive genotype. Therefore the number of offsprings with recessive-recessive genotype is one.
See the attached punnet square for more information
