In flowering plants, when a flower is fertilised by its own pollen or by pollen from another flower on the same plant, this is called self pollination. Self pollination most commonly leads to which of the following genetic outcomes in the plant population?

Introduction / Context:
Pollination is the transfer of pollen from the anther to the stigma. When this occurs within the same flower or between flowers on the same plant, it is called self pollination. When it occurs between different plants of the same species, it is called cross pollination. This question explores the genetic consequences of self pollination, especially its effect on the level of inbreeding and genetic variation in a plant population.

Given Data / Assumptions:

- The process considered is self pollination, not cross pollination. - The focus is on genetic outcomes such as inbreeding or outbreeding. - We assume repeated self pollination over several generations. - Terms like inbreeding and outbreeding are used in their standard genetic sense.

Concept / Approach:
Inbreeding occurs when genetically related individuals mate, increasing the chance that offspring receive identical copies of alleles from both parents. Self pollination is an extreme form of inbreeding because the pollen and ovule originate from the same genetic individual. Over generations, selfing increases homozygosity, leading to a more uniform genetic makeup. Outbreeding, in contrast, involves unrelated individuals and tends to increase genetic diversity. Therefore, self pollination is strongly associated with inbreeding, not outbreeding.

Step-by-Step Solution:
1. Recognise that in self pollination, the male and female gametes come from the same plant, often the same flower. 2. Because both gametes share the same genetic origin, offspring are more likely to inherit identical alleles from both sides, increasing homozygosity. 3. This repeated mating between genetically identical or very similar individuals is the definition of inbreeding. 4. Over many generations of self pollination, recessive alleles become more frequently expressed, and the level of genetic variation within the line is reduced. 5. The term outbreeding refers to mating between unrelated or distantly related individuals, which does not occur under strict self pollination. 6. There is no standard genetic concept called over breeding or rare breeding that specifically describes the effect of self pollination. 7. Therefore, self pollination most directly leads to inbreeding.

Verification / Alternative check:
Plant breeders often use self pollination to create pure lines, which are highly homozygous and genetically uniform. This practice is common in the development of inbred lines of crops such as wheat and rice. These pure lines can then be crossed with other lines to create hybrids that show hybrid vigour. The need for deliberate cross between inbred lines shows that self pollination alone tends to reduce variation and increase homozygosity, which is the hallmark of inbreeding.

Why Other Options Are Wrong:
- Over breeding, with unlimited increase in offspring fitness: Self pollination does not guarantee increasing fitness; in fact, it may expose harmful recessive traits due to inbreeding. - Outbreeding, with increased genetic mixing between unrelated plants: Outbreeding requires crossing between different individuals, which is the opposite of self pollination. - Rare breeding, with a progressive decline in seed production: Self pollination can sometimes maintain seed production, especially in self compatible species, and is not defined as rare breeding.

Common Pitfalls:
Students sometimes assume that self pollination is always harmful or always beneficial. In reality, its main predictable effect is increased homozygosity and inbreeding. Whether this is good or bad depends on context. Some plants are adapted to self pollinate and maintain stable, well adapted genotypes, while others rely on cross pollination for genetic diversity. Remember that the genetic term most directly linked to self pollination is inbreeding.

Final Answer:
Self pollination most commonly leads to inbreeding, with increased homozygosity in the plant population over generations.