A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as: (a) TTWW (b) TTww (c) TtWW (d) TtWw


Gunpreet, Subject Matter Expert at Edumarz

Answer: The correct option is (c) TtWW

Based on Mendelian experiments, we know that a cross between a homozygous dominant parent and a homozygous recessive parent results in an F1 generation of all dominant offspring which would be heterozygous because each will receive genes from both parents. However, in the above statement, it has been said that the F1 progeny consists of plants that bore all violet flowers but half of this progeny is tall and half is short. All plants bearing violet flowers show that violet is the dominant flower colour(WW) while white is recessive(ww).

If white is recessive then the genotype of short pea plants bearing white flowers (one parent) must be ttww (homozygous recessive), because recessive genes express themselves in homozygous conditions only.

In progeny, all plants bear violet flowers, which means the second parent is homozygous dominant for violet colour (WW). Now because half of the progeny is tall and half is short, it means this parent plant is heterozygous (Tt). Thus the genotype of the tall parent plant should be TtWW.

Parents:           TtWW (Tall plant, violet flower)   ╳     ttww (Short plant, white flower)


Gametes:         TW, tW                                        ╳     tw

F1 Progeny:    TtWw (Tall plant, violet flower)    and    ttWw (Short plant, violet flower)

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