Question

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 suggested that the genetic makeup (or genotype) of the tall parent can be depicted as

(a) TTWW (b) TTww (c) TtWW (d)TtWw

Give the reason for your choice.

Answer 1

(c) TtWW

The genetic makeup of the tall parent can be depicted as TtWW. Since all the progeny has violet flowers so the genotype of the tall plant for violet flower colour should be WW. Secondly, since almost half of the progeny is short which suggests that the tall plant is not pure and possesses the genotype Tt.

So if the cross is made between the tall parent TtWW and other parent ttww, the genotype of the progeny obtained is

TtWw (8): ttWw (4): ttWw (4)

All the progeny bears violet flowers but half of them are tall and half are short.

The condition explained is a dihybrid cross which involves two characters in a single plant.

In the given cross, the parent pea plants are of two types:

1. Tall plants with violet flowers
2. Short plants with white flowers

So, the genotype of the parents could be:

1. Tall plants with violet flowers: TTWW or TtWw
2. Short plants with white flowers: ttww

Since, all the progeny bore violet flowers, it implies that the tall plant with violet flowers has genotype ‘WW’ for violet flower colour.

Since, the progeny obtained is both tall and short, the parent plant was not a pure tall plant and bears genes that determine short height of the plant. Therefore, the genotype of the plant with respect to height would be ‘Tt’.

So, if a cross is carried out between tall parent with violet flowers (TtWW) and short parent with white flowers (ttww), the progeny obtained is TtWw (8):ttWw (4):ttWw(4).

All the progeny bear violet flowers but half of them are tall and half are short.