Question

Mirabilis jalapa resembles a good example of
(a)Complete dominance
(b)Plastid inheritance
(c)Mitochondrial inheritance
(d)None of the above

Answer 1

Extranuclear or cytoplasmic inheritance is defined as the transmission of genes that are not part of the nucleus i.e. they are genes from the cytoplasm. It is seen in the case of inheritance of genes from the mitochondria, chloroplasts, viruses, or bacteria.

Complete answer:
The plant Mirabilis jalapa resembles a good example of plastid inheritance. Plastids are cytoplasmic organelles found in the cells of plants. There are many types of plastids in a cell but the most important type is the chloroplast which contains chlorophyll pigments in it, thus photosynthesis takes place in it. Chloroplasts are able to divide independently of the nucleus as they have their own DNA. As plastid is part of the cytoplasm, the zygote receives cytoplasm from the female gamete (mother’s cell) and thus genes of the plastid are inherited from the mother. The same is seen in the case of Mirabilis jalapa where some characters are seen in the plant due to plastid genes.

Additional Information: -The characters seen in the Mirabilis jalapa due to plastid genes are in kinds of branches that are completely green, completely pale green, and variegated.
-It is seen that whatever the branch associated with the female flower is, the offspring also has the same branch indicating that plastid genes are inherited from the mother.
-In humans, only mitochondrial and nuclear DNA is present as plastids are not seen in animal cells.
-The mitochondrial DNA is circular in shape whereas the nuclear DNA is linear.
-Mitochondrial DNA only has 37 genes whereas nuclear DNA has more than 20,000 genes.2
-Mitochondrial DNA is again inherited just from the mother whereas the nuclear DNA is inherited 50% from the mother and 50% from the father.
So, the correct option is ‘Plastid inheritance’.

Note: -Mitochondria and chloroplasts are semiautonomous organelles which means they have their own DNA and protein synthesis machinery but are dependent on the nucleus for some functions.
-Mitochondria and chloroplasts are known as endosymbionts which means that they are prokaryotic bacteria that started living inside the eukaryotic cells as symbionts.
-A structure analogous to mitochondria is seen in prokaryotes known as mesosomes.