Alleles that grant some evolutionary advantage (reproduction and survival) may overcome almost any reproductive barrier, and may eventually become fixed in all exposed gene pools (Piálek and Barton 1997; Morjan and Rieseberg 2004).
The females' ability may effectively serve as a reproductive barrier that is important in speciation, the divergence of new species from existing ones.
Hybrid weakness is a reproductive barrier.
A reproductive barrier may have developed between the annual and perennial populations.
The observed ratio did not fit the expected ratio 1 1 (χ2 = 11.57, P = 0.00067), probably because of the reproductive barrier, as described above.
We inferred that the deviation from the expected ratio was probably caused by the linkage between HWA1 gene and gametophytic reproductive barrier gene(s), which is often found in crosses between Indica and Japonica (see Discussion).
In another case, causal genes of reproductive barrier in rice, which had been thought to be allelic before, proved to be a complex of two very tightly linked genes.
Many postzygotic reproductive barrier forms have been reported in rice (Oryza sativa), such as hybrid weakness (e.g., Oka 1957), hybrid pollen sterility (e.g., Long et al. 2008), and hybrid sterility causing female gamete abortion (e.g., Chen et al. 2008).
For instance, under the BSC, species status is achieved only when a reproductive barrier has evolved, which is not a requirement of the Ecological Species Concept (EcSC Van Valen 1976).
I give a brief history of the radiation, examine the process of divergence by natural selection over time, and then consider the nature of the reproductive barrier to gene flow between closely related species.
Triploid varieties have an additional reproductive barrier in that 3 sets of chromosomes cannot be divided evenly during meiosis, yielding unequal segregation of the chromosomes (aneuploids).
