Cytoplasmic inheritance in plants refers to the transmission of traits controlled by genes found outside the nucleus, specifically in the cytoplasm — in organelles such as mitochondria and chloroplasts.
Here’s how it works:
- Where the genes are located –
Most genes are found in the nucleus, but chloroplasts and mitochondria also have their own small DNA molecules. These contain genes that control important functions like photosynthesis (in chloroplasts) and respiration (in mitochondria). - Inheritance through the cytoplasm –
During fertilization, most of the cytoplasm (and its organelles) comes from the egg cell rather than the pollen.
This means that traits controlled by chloroplast or mitochondrial DNA are usually inherited only from the mother (maternal inheritance). - How it differs from Mendelian inheritance –
Unlike nuclear genes, cytoplasmic genes do not follow Mendel’s laws of segregation or independent assortment because they are not located on chromosomes in the nucleus. - Example in plants –
- Leaf color variegation in Mirabilis jalapa (the four o’clock plant): The leaf color (green, white, or variegated) depends on the type of chloroplasts inherited from the mother plant.
- Male sterility in maize and rice: Controlled by mitochondrial genes, this trait is used in hybrid seed production.
- Importance of cytoplasmic inheritance –
- Helps in understanding non-Mendelian inheritance patterns.
- Used in crop breeding to develop hybrids and improve yield.
- Explains energy-related traits, since mitochondria and chloroplasts are vital for metabolism and photosynthesis.
- Possible mutations –
Mutations in chloroplast or mitochondrial DNA can lead to defects in photosynthesis, respiration, or growth, affecting plant performance.
In summary:
Cytoplasmic inheritance in plants occurs when genes in chloroplasts or mitochondria are passed on, usually from the mother plant, to the offspring. It results in traits that do not follow normal Mendelian patterns and plays an important role in plant physiology and breeding.