A child receives a tall beautiful plant as a birthday gift from his fa

A child receives a tall beautiful plant as a birthday gift from his father with a quiz. The father asked her how she would verify whether this tall plant was the progeny of both the tall parents or one tall and one short parent plant. She could verify this through

cross-pollination
self-pollination
tissue culture
negative propagation
This question was previously asked in
UPSC CDS-1 – 2021
She could verify this through cross-pollination.
To determine the genotype of a plant showing a dominant phenotype (tall), the standard method is a test cross. A test cross involves cross-pollinating the plant with a homozygous recessive plant (short). If the progeny includes any short plants, the tall parent must be heterozygous (Tt). If all progeny are tall, the tall parent is likely homozygous dominant (TT). This method allows differentiation between potential parental genotypes (Tall x Tall vs. Tall x Short leading to different progeny genotypes).
Self-pollination could also provide clues (a heterozygous plant would produce some recessive offspring upon selfing), but a test cross is more definitive for confirming homozygosity vs. heterozygosity. Tissue culture is a propagation technique, and ‘negative propagation’ is not a standard biological term in this context.