Question

Briefly explain maternal inheritance in the variegated four o'clock plant.

Answer 1

Four o’clock plants have leaves of different color on different branches on same tree i.e., green, variegated (white and green) or white leaves. When a cross was made between flowers from different branches with different leaf color on the female plant with pollen obtained from flowers of the three different colored leaves. From this crossing, obtained progeny always exhibited the color of the leaf of the female. If the female flower was taken from green branch the progeny were green; when female flower from white then progeny were green and when female flower was taken from variegated (leaf) branch then progeny were also variegated. From this experiment we can see that the phenotype of the progeny is always similar to female parent and there is no any character from male parent.

Green female x Green male = Green progeny

White female x Green male = White progeny

Green female x White female = Green progeny

Variegated female x Green male = Green and white progeny

Green female x Variegated female = Green progeny

White female x Variegated female = White progeny

As we know that the gene responsible for leaf coloration are present in chloroplast within the cytoplasm and cytoplasm is only contributed by female parent. In zygote   cytoplasm comes from egg cell i.e., female parent and nucleus from male parent. Therefore any genes present in the cell organelles of the cytoplasm are responsible for maternal inheritance.  Variegated leaves have leaf two types of chloroplasts i.e., normal green chloroplast and chloroplast that lack chlorophyll pigment. As we know that chloroplasts are genetically autonomous organelles, it has small circular naked DNA which carries genes responsible for regulation of chloroplast structure and function.