A pure tall garden pea plant was crossed with a pure dwarf plant. The plant produced 400 seeds. The seeds were sown to produce plants. The phenotype of the plants in next generation will be :-
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → All tall
Tall (T) is dominant over dwarf (t). A pure tall plant is TT and a pure dwarf plant is tt.
Cross: TT × tt
Gametes: T and t
Every seed of the cross is Tt: the F1 generation
All 400 plants grown from these seeds are Tt, and they show the dominant trait: all are tall.
Option (2) All dwarf — Incorrect. Dwarf is recessive; it shows only in tt plants, and none are formed here.
Option (3) 300 tall and 100 dwarf plants — Incorrect. The 3 : 1 ratio appears in the F2, when the F1 plants are self-pollinated. These seeds are only F1.
Option (4) All plants of intermediate height — Incorrect. An in-between form appears in incomplete dominance, as in the snapdragon flower colour. Height in pea shows complete dominance.
NCERT Extract:
Inheritance of One Gene – “Let us take the example of one such hybridisation experiment carried out by Mendel where he crossed tall and dwarf pea plants to study the inheritance of one gene (Figure 4.2). He collected the seeds produced as a result of this cross and grew them to generate plants of the first hybrid generation. This generation is also called the Filial1 progeny or the F1. Mendel observed that all the F1 progeny plants were tall, like one of its parents; none were dwarf (Figure 4.3). He made similar observations for the other pairs of traits – he found that the F1 always resembled either one of the parents, and that the trait of the other parent was not seen in them.”
Figure 4.3 Diagrammatic representation of monohybrid cross