| Date | May 2015 | Marks available | 2 | Reference code | 15M.3.HL.TZ1.1 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Outline | Question number | 1 | Adapted from | N/A |
Question
There are many closely related Canis species in North America including the grey wolf (C. lupus), eastern wolf (C. lycaon) and western coyote (C. latrans). Hybridization can occur between members of these species.
For example, during the last 100 years, hybridization has occurred between western coyotes (C. latrans) and eastern wolves (C. lycaon) in the area of Ontario shown by a star in the map shown below.
Genetic evidence for hybridization is based on identification of haplotypes (combinations of linked alleles in clusters of similar genes) that exist in mitochondrial DNA (mtDNA) of Canis populations. The populations in this study were the Minnesota-northwestern wolf, southern Ontario coyote and northeastern coyote. Assume that all animals in each Canis population have the same mtDNA haplotypes.
Outline the genetic evidence that Canis populations have hybridized.
Compare the genetic data for southern Ontario coyotes and northeastern coyotes.
State with a reason whether the genetic evidence shows that the western coyote and the grey wolf have overlapping ranges.
The northeastern coyote has more wolf-like skull features than the southern Ontario coyote. Suggest a reason for this difference.
Discuss briefly whether there is genetic evidence to show a common ancestor for the Minnesota-northwestern wolf, the southern Ontario coyote and the northeastern coyote.
Markscheme
a. (all three) Canis populations show a mixture of haplotypes from two (or more) origins;
b. Minnesota-northwestern wolves have a mixture of haplotypes from grey wolf/C. lupus and eastern wolf/C. lycaon;
c. southern Ontario coyote has mixture of haplotypes from western coyote/C. latrans and eastern wolf;
d. northeastern coyote has mixture of haplotypes from western coyote/C. latrans and eastern wolf;
a. both contain haplotypes C1, C9 and C19;
b. C19 haplotype in greater proportion in northeastern coyotes / vice versa;
c. C9 haplotype in greater proportion in southern Ontario coyotes / vice versa;
d. C1 in smaller proportion in southern Ontario than northeastern coyotes / vice versa;
e. southern Ontario coyotes / northeastern coyotes have more haplotypes from coyotes than wolves;
f. fewer haplotypes from other sources in northeastern coyotes / vice versa;
no overlapping ranges since no haplotypes/C9, C19 from western coyotes present with haplotype/C22 from grey wolf in any of the hybrids.
northeastern coyote has greater proportion of C1/ haplotype from (eastern) wolf (than southern Ontario coyote)
a. all three show evidence that the eastern wolf was their ancestor/all have haplotypes from the eastern wolf;
b. southern Ontario and northeastern coyotes have different eastern wolf haplotypes from the Minnesota northwestern wolf / southern Ontario and northeastern coyotes have C1 while the Minnesota northwestern wolf has C3 and C13;
Examiners report
There were some comments on the G2 forms regarding the graphs for this question being difficult to analyze or confusing. The names of the wolves and coyotes did sometimes lead to confusion. One problem was that many candidates misread the diagram and thought it showed proportions of areas instead of proportions of haplotypes. Despite this, Question D1 often scored fairly well.
Most candidates were able to get 1 mark for either seeing that all Canis populations showed a mixture of haplotypes from 2 or more origins or for giving an example to support this. Only the better candidates were able to get 2 marks.
There were some comments on the G2 forms regarding the graphs for this question being difficult to analyze or confusing. The names of the wolves and coyotes did sometimes lead to confusion. One problem was that many candidates misread the diagram and thought it showed proportions of areas instead of proportions of haplotypes. Despite this, Question D1 often scored fairly well.
Most candidates again were able to get at least 1 mark, often for stating that both species had the same 3 haplotypes. Many were also able to get a second mark for telling how they differed in the proportion of these haplotypes.
There were some comments on the G2 forms regarding the graphs for this question being difficult to analyze or confusing. The names of the wolves and coyotes did sometimes lead to confusion. One problem was that many candidates misread the diagram and thought it showed proportions of areas instead of proportions of haplotypes. Despite this, Question D1 often scored fairly well.
Only better candidates were able to see there was no overlap in ranges and use the data to explain why.
There were some comments on the G2 forms regarding the graphs for this question being difficult to analyze or confusing. The names of the wolves and coyotes did sometimes lead to confusion. One problem was that many candidates misread the diagram and thought it showed proportions of areas instead of proportions of haplotypes. Despite this, Question D1 often scored fairly well.
This was often answered well with many able to get a mark for suggesting that more of the C1 haplotype gave more wolf-like features to the northeastern coyote.
There were some comments on the G2 forms regarding the graphs for this question being difficult to analyze or confusing. The names of the wolves and coyotes did sometimes lead to confusion. One problem was that many candidates misread the diagram and thought it showed proportions of areas instead of proportions of haplotypes. Despite this, Question D1 often scored fairly well.
Many obtained 1 mark for seeing that the eastern wolf was a common ancestor but few were able to get a second mark.
