Comparison Table: Normal vs Special Reproduction Modes
| Mode | Fertilization? | Seed Formed? | Fruit Formed? | Genetic Outcome | Example |
|---|---|---|---|---|---|
| Normal sexual reproduction | Yes (double fertilization) | Yes | Yes | Variable offspring | Mango, wheat |
| Apomixis | No | Yes | Yes (often) | Clonal offspring (identical to parent) | Citrus, dandelion |
| Parthenocarpy | No | No (seedless) | Yes | No offspring (no seeds) | Banana, seedless grapes |
| Polyembryony | Yes (+ nucellar) | Yes (multiple embryos) | Yes | Mixed (sexual + clonal embryos) | Citrus, Opuntia |
Apomixis Types
- Diplospory: Megaspore mother cell develops into embryo sac without meiosis (unreduced embryo sac).
- Apospory: Nucellar cells develop into an embryo sac (without meiosis).
- Adventive embryony: Nucellar or integument cells develop directly into embryos within a seed alongside a sexually produced embryo (seen in Citrus — hence polyembryony).
Polyembryony Mechanisms
- Nucellar (adventive): Nucellus cells → additional embryos alongside the zygote embryo (e.g., Citrus — produces uniform disease-free rootstocks)
- Cleavage: Proembryo splits into multiple embryos
- Multiple fertilizations: More than one egg fertilized (uncommon)
Agricultural Exploitation
- Citrus polyembryony produces uniform nucellar seedlings used as disease-free rootstocks
- Apomictic varieties in mango and Citrus allow true breeding from seeds
- Parthenocarpy exploited commercially for seedless fruit production