Understanding Extranuclear Heredity and Non-Mendelian Inheritance Patterns
Cytoplasmic inheritance refers to the transmission of genetic material that occurs outside the nucleus, primarily through the cytoplasm of the egg (ovum). This type of inheritance is associated with organelles like mitochondria and chloroplasts, which contain their own DNA. Unlike nuclear DNA, which follows Mendelian inheritance patterns, cytoplasmic inheritance exhibits maternal (uniparental) transmission, as the ovum contributes most of the cytoplasm to the zygote while the sperm does not.
Inheritance occurring outside the nucleus, encompassing all genetic material transmitted through cytoplasmic organelles rather than chromosomes.
The primary characteristic of cytoplasmic inheritance where genetic traits are inherited exclusively or predominantly from the female parent through the egg cytoplasm.
Inheritance patterns that do not follow Mendel's laws, showing uniparental transmission and lack of segregation ratios typical of nuclear genes.
Genetic transmission involving DNA located outside chromosomes, specifically in organellar genomes of mitochondria and chloroplasts.
The inheritance of traits controlled by genes present in cellular organelles such as mitochondria (animals) and chloroplasts/plastids (plants).
Specific form of cytoplasmic inheritance involving plastids and chloroplasts in plants, controlling leaf pigmentation and other chloroplast-dependent traits.
(Four O'Clock Plant)
First documented by Carl Correns in 1908-1909, leaf variegation in Mirabilis jalapa provided the earliest conclusive evidence for cytoplasmic inheritance.
The phenotype of progeny depends entirely on the female parent:
Variegation results from random segregation of mutant and normal chloroplasts during cell division. Different branches develop different ratios of green and defective plastids through this somatic segregation.
(Zea mays)
Cytoplasmic male sterility (CMS) in maize is controlled by genes in mitochondrial DNA and represents a crucial example of extranuclear inheritance with significant agricultural implications.
Male sterility is the failure to produce functional anthers, pollen, or functional male gametes, while the plant remains otherwise healthy and can function as a female parent.
Male sterility is inherited maternally through the egg cytoplasm:
Cytoplasmic male sterility in maize has revolutionized plant breeding by eliminating the need for manual emasculation in hybrid seed production, making large-scale hybrid corn breeding economically feasible.