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Comparison of Cytoplasmic and Nuclear Inheritance
| Feature | Cytoplasmic Inheritance | Nuclear Inheritance |
|---|---|---|
| Definition | Transmission of traits via genes located in organelles like mitochondria or chloroplasts. | Transmission of traits via genes in the nuclear chromosomes. |
| Location of Genes | Found in mitochondrial or chloroplast DNA (extranuclear). | Found in chromosomal DNA inside the nucleus. |
| Inheritance Pattern | Maternal (zygote inherits cytoplasm from the egg). | Biparental (genes inherited from both parents). |
| Type of DNA | Circular DNA in organelles. | Linear DNA organized into chromosomes. |
| Segregation | Non-Mendelian; no segregation during meiosis. | Mendelian; follows laws of segregation and independent assortment. |
| Examples | Male sterility in maize, variegated leaves in Mirabilis jalapa. | Mendel’s pea traits, human eye color. |
Types of Cytoplasmic Inheritance
| Type | Explanation | Example | Key Features |
|---|---|---|---|
| Chloroplastic Inheritance | Traits determined by genes in chloroplast DNA. | Variegated leaves in Mirabilis jalapa |
– Mutation in chloroplast DNA. – Results in green (normal chloroplasts), white (mutated chloroplasts), or variegated leaves (mixture of normal and mutated chloroplasts). |
| Mitochondrial Inheritance | Traits determined by genes in mitochondrial DNA. | Male sterility in maize |
– Mutations in mitochondrial DNA disrupt energy production for pollen development. – Leads to failure in anther or pollen formation. |
Cytoplasmic Inheritance: Key Examples
| Example | Details |
|---|---|
| Variegated Leaves in Mirabilis jalapa |
– Phenomenon: Leaves exhibit green (normal chloroplasts), white (mutated chloroplasts), or variegated (mix of both). – Cause: Mutation in chloroplast DNA affecting chlorophyll production. – Inheritance: Maternal (zygote inherits chloroplasts from the egg). – Significance: Demonstrates non-Mendelian inheritance via organelle DNA. |
| Male Sterility in Maize |
– Phenomenon: Male plants fail to produce functional pollen. – Cause: Mutations in mitochondrial DNA disrupt energy production during pollen development. – Rare Pollen: Occasionally, male-sterile plants produce rare viable pollen. – Inheritance: Maternal (mitochondria inherited from the egg). – Application: Used in agriculture for hybrid seed production. Eliminates manual emasculation. |
Variegated Leaves in Mirabilis jalapa
| Aspect | Details |
|---|---|
| Phenomenon | Leaves show patches of green, white, or a mixture (variegation). |
| Cause |
– Mutation in chloroplast DNA: – Green patches: Normal chloroplasts. – White patches: Non-functional chloroplasts (no chlorophyll). |
| Inheritance Pattern |
Maternal: Zygote inherits cytoplasm (and chloroplasts) from the egg. – Normal egg: Offspring are green. – Mutated egg: Offspring are white. – Heteroplasmic egg: Heteroplasmy (mixture of normal and mutated chloroplasts) results in variegation. |
| Significance | Non-Mendelian inheritance. Demonstrates the role of organelle DNA in traits. |
Male Sterility in Maize
| Aspect | Details |
|---|---|
| Phenomenon | Male-sterile plants fail to produce functional pollen, leading to male sterility. |
| Cause | Mutations in mitochondrial DNA impair energy production required for pollen and anther development. |
| Inheritance Pattern | Maternal: Mitochondrial DNA is inherited from the egg. Sperm does not contribute mitochondria. |
| Rare Pollen Formation | Male-sterile plants occasionally produce rare, viable pollen capable of fertilizing female plants. |
| Fertilization Process |
– Rare viable pollen from male-sterile plants fertilizes eggs (either male-fertile or male-sterile plants). – Offspring inherit maternal cytoplasm, thus retaining male sterility. |
| Backcrossing |
– Backcrossing involves repeated fertilization of male-fertile plants using rare pollen from male-sterile plants. – Male sterility persists due to the maternal inheritance of mitochondrial DNA. |
| Significance | Male sterility persists even after many backcrosses, allowing for the continuous use of sterile lines in agriculture. |
| Applications |
– Simplifies hybrid seed production. – Eliminates the need for labor-intensive manual emasculation (removal of male parts). |
Cytoplasmic Inheritance: Key Examples (Summary)
| Example | Details |
|---|---|
| Variegated Leaves in Mirabilis jalapa |
– Phenomenon: Leaves exhibit green (normal chloroplasts), white (mutated chloroplasts), or variegated (mix of both). – Cause: Mutation in chloroplast DNA affecting chlorophyll production. – Inheritance: Maternal (zygote inherits chloroplasts from the egg). – Significance: Demonstrates non-Mendelian inheritance via organelle DNA. |
| Male Sterility in Maize |
– Phenomenon: Male plants fail to produce functional pollen. – Cause: Mutations in mitochondrial DNA disrupt energy production during pollen development. – Rare Pollen: Occasionally, male-sterile plants produce rare viable pollen. – Inheritance: Maternal (mitochondria inherited from the egg). – Application: Used in agriculture for hybrid seed production. Eliminates manual emasculation. |
