Question

A particular mutation in a species of plant leads to variegation in its leaves (part of each leaf is white, while part is green). A plant breeder takes pollen from a green plant and pollinates a variegated plant. All resulting offspring are variegated. The breeder then takes pollen from a variegated plant and pollinates a green plant. All resulting offspring are green. What is going on?\

Answer 1

In the first case the male plant is green and the female plant is variegated. Their progeny consists of only variegated plants.

In the second case the male plant is variegated and the female plant is green. Their progeny consists of only green plants.

It can be observed that the progeny always shows the leaf color phenotype of the female parent. This is a case of maternal inheritance. After fertilization, the embryo has mitochondria and chloroplast from the female parent. This happens because the male gamete is very small and devoid of any organelle whereas the female gamete is big and carries its organelles. Out of all the organelles in female gamete, mitochondria and chloroplast have their own DNA.

Here, the gene for leaf color is probably located on chloroplast's DNA since it contains chlorophyll which is responsible for leaf color. If the female parent has green leaves, it will pass the gene for it to the next progeny as well via organellar DNA. This way the progeny will always have the same leaf color as the female parent.