Question

In a Four o’clock plant, normal leaves (A) and variegated leaves (B) occur in different plants. If (B) male is crossed with (A) female, the hybrid has normal leaves, but when (B) female is crossed with (A) male, the hybrid has variegated leaves. It is a case of.
(a) Mutation
(b) Cytoplasmic inheritance
(c) Complementary genes
(d) Supplementary genes

Answer 1

 Hint: In the given examples, both the hybrids have leaf traits from the female. This type of inheritance only from the mother is also seen in the case of mitochondria in humans. This type of transfer of characters was first discovered by Correns in Mirabilis jalapa.

Complete Step by Step Answer:
This type of inheritance of characters only from the mother is known as cytoplasmic inheritance. It is the transmission of genes that occur outside the nucleus of the cells. It is seen in most eukaryotic organisms and is commonly known to occur in cytoplasmic organelles such as mitochondria and chloroplasts and sometimes from cellular parasites such as viruses or bacteria.
The extranuclear types of DNA that are present as mitochondrial DNA or in other forms replicate independently of the nucleus. The extranuclear DNA present in the mitochondria and chloroplasts replicate independently of cell division. They replicate to compensate for a cell's increasing energy needs. Since they replicate independently the recombination of genes is rarely found in them, contrary to nuclear genomes in which recombination is prevalent.
In most organisms, the male gamete is very small as compared to the female gamete and is mostly occupied by the nucleus. Hence, the cytoplasm and the cytoplasmic genome is mostly inherited from the mother. Hence, this kind of inheritance is called cytoplasmic inheritance.
So, the correct answer is, “Cytoplasmic inheritance.”

Note:
- Cytoplasmic inheritance is the reason for the inheritance of mitochondrial diseases from the mother and not from the father.
- In some cases, there may be an extranuclear transmission of viral genomes and pathogens, not by direct inheritance but through perinatal transmission. In these cases, the viral material is transferred from the mother to the child in the bloodstream or through breastfeeding.
- In some cases, such as in the yeast, both the haploid gametes are of the same size and contribute an equal amount of cytoplasm. In such cases, the cytoplasmic inheritance may be biparental in nature.