Question
What is apomixis? How does it differ from normal sexual reproduction in flowering plants? Explain polyembryony with an example. Why is apomixis agriculturally significant?
(NCERT Class 12 — directly asked in NEET)
Solution — Step by Step
Apomixis is the production of seeds without fertilisation. The embryo develops from the diploid cells of the ovule (not from a zygote formed by fusion of gametes).
Three types:
- Diploid egg cell forms without meiosis (the megaspore mother cell skips meiosis, remaining diploid) → develops directly into an embryo
- Nucellar cells (diploid, surrounding the embryo sac) protrude into the embryo sac and develop into embryos
- Adventive embryony — embryos develop from cells of the nucellus or integuments
| Feature | Sexual reproduction | Apomixis |
|---|---|---|
| Meiosis | Required | Bypassed |
| Fertilisation | Required (pollen + egg) | Not required |
| Offspring genetics | Genetically diverse (recombination) | Genetically identical to parent (clones) |
| Seed formation | From zygote (2n) | From unfertilised egg or nucellar cells |
Polyembryony is the occurrence of more than one embryo in a single seed.
In citrus fruits (orange, lemon), some nucellar cells surrounding the embryo sac divide and develop into additional embryos alongside the normal zygotic embryo. When the seed germinates, multiple seedlings emerge.
The nucellar embryos are genetically identical to the parent (clones), while the zygotic embryo is a hybrid. This is why citrus seeds often produce several seedlings, most of which are maternal clones.
Apomixis is highly valuable in agriculture because:
- Preserves hybrid vigour — hybrid seeds are expensive to produce each season because the F2 generation loses hybrid vigour. If a hybrid could reproduce by apomixis, every generation would be genetically identical to the superior F1 hybrid.
- Reduces cost — farmers wouldn’t need to buy new hybrid seeds every year
- Uniform crops — all plants are genetically identical, ensuring consistent quality
Researchers are working to introduce apomictic genes into crop plants — this would revolutionise hybrid seed production.
Why This Works
Apomixis is nature’s way of cloning through seeds. By bypassing meiosis and fertilisation, the plant produces offspring that are genetically identical copies of itself. This is advantageous when the parent has a successful genotype — why risk genetic shuffling when the current combination works well?
Polyembryony adds another layer — multiple embryos in one seed increase the chance that at least one will successfully germinate. In citrus, the nucellar embryos often outcompete the zygotic embryo, ensuring the parent genotype is faithfully reproduced.
Alternative Method — Quick Comparison
For NEET, remember the key distinction:
- Apomixis = seed production without fertilisation (asexual reproduction through seeds)
- Parthenocarpy = fruit development without fertilisation (seedless fruits — banana, grape)
These are different concepts. Apomixis produces seeds (with embryos). Parthenocarpy produces fruits without seeds. NEET has tested this distinction — don’t mix them up.
Common Mistake
Students often say “apomixis is the same as vegetative reproduction.” It’s not — vegetative reproduction uses roots, stems, or leaves (no seeds involved). Apomixis specifically involves seed formation without fertilisation. The seed looks normal from outside, but the embryo inside is a clone. Also, polyembryony is NOT the same as having multiple seeds — it’s multiple embryos within a single seed.