Final answer:
When dominant phenotype individuals are crossed and all offspring also exhibit the dominant phenotype, the logical genotype of the parents could either be both homozygous dominant (AA) or one parent homozygous dominant (AA) and the other heterozygous (Aa). The correct option is E. both B and C.
Step-by-step explanation:
If individuals exhibiting a dominant phenotype are crossed and produce only offspring with the dominant phenotype, we can deduce the genotype of the parents based on our understanding of Mendelian genetics. Given that the dominant phenotype is expressed whether the individual is homozygous dominant (AA) or heterozygous (Aa), the recessive phenotype (aa) can only be expressed if an individual has two recessive alleles.
Therefore, if all offspring show the dominant phenotype, it suggests that no recessive alleles were passed on to them. This could occur if either both parents are homozygous dominant (AA) or one parent is homozygous dominant (AA) and the other is heterozygous (Aa).
Taking into consideration that if two heterozygous individuals (Aa) were crossed, there would be a 25% chance of producing a homozygous recessive offspring (aa), which contradicts the outcome stated in the student's question. Consequently, the correct genotype of the parents cannot be two heterozygous individuals.
The logical genotypes would instead be either both parents being homozygous dominant (AA) or one parent being homozygous dominant and the other heterozygous (AA x Aa).
In summary, considering all possibilities and acknowledging that no offspring with the recessive phenotype were produced, the two most likely scenarios for the parents' genotypes are that both parents are homozygous dominant or one is homozygous dominant and the other is heterozygous. Therefore, the correct answer to the student's question is: E. both B and C.