Bison are a type of large wild cattle. Ancestors of modern bison appeared in Asia 2.5 million years ago. This ancestral bison species increased its range into Europe and North America. While the ancestral species is now extinct, its descendants include Bison bonasus, the European bison, and Bison bison, the American bison. [Figure 5.1] shows an American bison.

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

1. [4] any four from: 1 geographical isolation / barrier qualified ; Ignore separation 2 no, interbreeding / gene flow (between European and American populations); Ignore reproductive isolation here (needs to be late on in process) 3 different, environmental (conditions) / selection pressures ; 4 random / different, mutations ; 5 different, alleles selected for / gene pool / changes in allele frequency ; 6 populations have different, morphological / physiological / behavioural, features; 7 after, a long time / many generations, reproductive isolation occurs / cannot interbreed to produce fertile offspring; 8 allopatric (speciation);
2. [3] any three from: 1 not possible / difficult, to come to a (reliable) conclusion ; A AW 2 small difference in height / heights are similar (so natural selection not more important than genetic drift); 3 taller/lighter, bison could be an advantage in reaching higher vegetation (so natural selection may be important); 4 difference in mass, may not be due to genetic factors / may be due to nutrient value of diet / may be due to quantity of food, (so natural selection may not be important) ; 5 genetic drift (in ancestral population) may have led to, European bison being, taller / lighter or American bison being, shorter / heavier;
3. [3] 1 European bison has a, close / recent / common, ancestor with that of, cattle / Bos or European bison is more closely related to, cattle / Bos, (than to American bison); 2 European bison may have interbred with, cattle / Bos ; 3 mitochondria are inherited from, mother / female;
4. [4] any four from: 1 obtain / use, blood / cells / tissue / DNA ; 2 from, both species / cattle and European bison ; 3 use PCR to, replicate / amplify, DNA ; 4 use, electrophoresis (described) / DNA profiling / DNA fingerprinting, to see genetic differences / compare the banding (patterns) ; 5 sequence DNA and, count / identify, (percentage) difference / similarity or sequence DNA and compare the, nucleotide / base, sequence ; 6 use, genome / DNA, microarray; R for gene expression 7 ref. to bioinformatics / database / (computer) software ; 8 similarity indicates, close relationship / more recent split ; 9 if they can breed to produce (viable) offspring (they are closely related) ;