2019年11月IB生物SL真题下载-Paper2
1. 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. rufi pogon is a wild species from which they probably evolved.
(a) State the reason that O. sativa and O. rufi pogon are classifi ed as diff erent species.
To investigate whether the sub-species of cultivated rice evolved independently from the wild species, scientists analysed their chromosomes to fi nd areas with similar DNA base sequences. Wild species tend to have many diff erent alleles of genes present on each chromosome, but during the development of a crop plant by artifi cial selection from a wild species, this diversity drops considerably, increasing the base sequence similarity. The number of diff erent 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. rufi pogon 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.
(b) Determine which type of rice has the lowest overall diversity index.
(c) Compare and contrast the trends for O. rufipogon and O. sativa indica.
In another experiment, scientists retrieved genome sequences of the wild rice O. rufi pogon taken from a wide range of geographical sites (I, II and III) and those of the two sub-species of O. sativa from gene banks.
The pie charts, presented along with a cladogram, show the proportion of alleles for three genes which confer specifi c characteristics to O. sativa. Mutations can produce derived alleles that are diff erent from the original ancestral alleles. The control group represents wild rice species other than O. rufi pogon.
(d) State the proportion of the ancestral allele for the gene GS3 in the O. rufi pogon-III population.
(e) Distinguish between the proportion of ancestral and derived alleles for all three genes in O. sativa indica and O. sativa japonica.
(f) State one reason for having a control group.
(g) Using all of the data, discuss whether there is evidence that the two sub-species of O. sativa might have evolved independently from O. rufipogon.
2019年11月IB生物SL真题余下省略！
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