Self-incompatibility mechanisms prevent self-fertilization in flowering plants and reduce inbreeding by rejecting genetically similar or self pollen during pollination events.
Self-incompatibility is a genetic recognition system that prevents self-pollen from fertilizing ovules and thereby promotes cross-fertilization.
Matching incompatibility alleles in pollen and stigma can block pollen germination or pollen-tube growth. Compatible pollen from another plant can continue to the ovule.
Self-pollination increases inbreeding, which reduces genetic diversity and can reduce vigour by increasing expression of harmful recessive alleles. Rejecting self-pollen helps maintain variation within the species.
Pollen sharing the stigma's incompatibility class is rejected, while pollen carrying a different compatible class grows a tube and can fertilize the ovule.
Self-incompatibility is not pollen sterility or physical separation; the same pollen may function normally on a genetically compatible plant.
This objective is assessed through multiple choice.
Build the answer around this relationship: Self-incompatibility prevents inbreeding rather than decreasing variation.
Representative question
Cherry trees (Prunus avium) have two self-incompatibility alleles. What benefit do self-incompatibility alleles have?
They decrease genetic variation.
They prevent inbreeding.
They decrease the chances of mutations taking place within the gametes.
They prevent the plant from releasing pollen at certain times of the year.
B
Core D3.1 route: reproduction creates offspring, gametes or pollen move, fertilization or germination follows, and the consequence is variation, embryo formation, seed production, or successful early growth.
Core D3.1 exam questions usually combine reproduction strategy with gamete formation, fertilization, human cycles, IVF, plant pollination, or seed germination. Treat each answer as a route: name the process, say what moves or changes, then give the biological consequence.