The expression of genes for the production of milk in only females is a

In $Drosophila$,irregularities are observed during the differentiation of organs. For example,long appendages are formed in place of wings. Which gene is responsible for this?

When certain traits are inherited only from the mother,it is likely a case of .....

After crossing two plants,the male progeny is found to be sterile. This phenomenon is inherited maternally,and the cause lies in genes located in the ...

Extranuclear inheritance is observed in .......... .

In a cross between white-flowered parents,$F_1$ progeny was uniformly purple-flowered. The $F_2$ progeny showed a phenotypic ratio $9:7$ between purple-flowered and white-flowered plants. The above result indicates that the flower colour is controlled by