Question 19N.2.SL.TZ0.1b

Cultivated rice, Oryza sativa, is one of the most important human foods. The two main sub-species of cultivated rice are O. sativa indica and O. sativa japonica. O. rufipogon is a wild species from which they probably evolved.

To investigate whether the sub-species of cultivated rice evolved independently from the wild species, scientists analysed their chromosomes to find areas with similar DNA base sequences. Wild species tend to have many different alleles of genes present on each chromosome, but during the development of a crop plant by artificial selection from a wild species, this diversity drops considerably, increasing the base sequence similarity.
The number of different alleles of the genes on a chromosome can be represented by a diversity index. The following graph of part of chromosome 7 shows the diversity index of O. rufipogon and two varieties of cultivated rice, O. sativa indica and O. sativa japonica. The gene PROG1 allows the plant to stand upright, which is typical of cultivated rice. Its position is indicated by the vertical arrow on the graph.

[Source: He Z, Zhai W, Wen H, Tang T, Wang Y, Lu X, et al. (2011) Two Evolutionary Histories in the Genome of Rice:
the Roles of Domestication Genes. PLoS Genet 7(6): e1002100. https://doi.org/10.1371/journal.pgen.1002100]