2011年5月IB生物SL真题下载-Paper2

2011年5月IB生物SL真题下载-Paper2

1. PanI is a gene in cod fish that codes for an integral membrane protein called pantophysin. Two alleles of the gene, PanIA and PanIB, code for versions of pantophysin, that differ by four amino acids in one region of the protein. Samples of cod fish were collected from 23 locations in the north Atlantic and were tested to find the proportions of PanIA and PanIB alleles in each population. The results are shown in pie charts, numbered 1–23, on the map below. The proportions of alleles in a population are called the allele frequencies. The frequency of an allele can vary from 0.0 to 1.0. The light grey sectors of the pie charts show the allele frequency of PanIA and the black sectors show the allele frequency of PanIB.

(a) (i) State the two populations with the highest PanIB allele frequencies.

(ii) State the population in which the allele frequencies were closest to 0.5.

(b) Deduce the allele frequencies of a population in which half of the cod fish had the genotype PanIA PanIA, and half had the genotype PanIA PanIB.

 

The graphs below show the latitude and the mean surface sea temperature in June of the sampling locations and the frequency of the PanIA allele.

(c) State the relationship between

(i) latitude and the frequency of the PanIA allele.

(ii) mean surface sea temperature in June and the frequency of the PanIA allele.

(d) Suggest how natural selection could have caused the relationships shown in the graphs.

(e) The sites close to Iceland, at a latitude of 60–65°, had very varied allele frequencies, with both PanIA and PanIB occurring. The water at these sample sites was highly stratified,with much warmer water at the surface and much colder water below. Suggest reasons for both PanIA and PanIB alleles occurring at these sites.

(f) Using the data in this question, predict the effects of global warming on cod fish populations.

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