Final answer:
The correct genotypes of the individuals crossed in this Mendelian genetics problem are heterozygous (Tt) for the tall individual #1 and homozygous recessive (tt) for the test cross individual.
Step-by-step explanation:
The student is dealing with a Mendelian genetics problem involving the inheritance of the tall trait in pea plants. Individual #1, with phenotype "T" (tall), is test crossed, and the offspring shows equal representation of tall and short phenotypes. This indicates that individual #1 must have one dominant allele (T) and one recessive allele (t) for height, making its genotype heterozygous (Tt).
The organism used for the test cross is always homozygous recessive (tt) to ensure that any dominant phenotype in the offspring comes from the test individual. Since half of the offspring are tall and half are short, individual #1 must be Tt, and it is crossed with a tt individual to yield the observed 1:1 phenotypic ratio.
The correct answer to the student's question is b. Tt and tt.