A-LevelBiologySelection and evolution9700/41 · May/June 2020 · Q312 Marks

Cats are members of the Felidae family. Two genera of Felidae are Leopardus and Panthera. (a) The genus Leopardus consists of species of wild cats that are small and spotted. In 2013, biologists investigated the evolution of Leopardus tigrinus in South America. Fig. 3.1 shows the locations in South America of two populations of. L. tigrinus, population A and population B. [Figure 3.1] • Population A lives in grassland and desert habitats and population B lives in forest habitats. • The cats in population A have a lighter coat colour and a different pattern of spots from the cats in population B. • Genetic analysis shows that population A is genetically distinct from population B. • Population B has now been reclassified as a new species, L. guttulus.

(a)(i)Define the term species.[2]
(a)(ii)Explain how the two species, L. tigrinus and L. guttulus, have evolved from one original population in South America.[5]
(b)(i)Illegal trade threatens the survival of endangered species. Forensic tests can identify animal species from the DNA of their body parts, for example bones. Cat species differ in the number of repeats of bases C and A (CA repeats) within one particular region of DNA, known as Ple46. Table 3.1 shows the number of repeats in Ple46 for three endangered cat species. [Table 3.1] Gel electrophoresis is used to estimate the length of Ple46 in a sample of DNA to check whether the sample comes from one of the endangered cat species in Table 3.1. Outline how gel electrophoresis is carried out to confirm whether the sample comes from one of these endangered cat species.[3]
(b)(ii)Customs officials are responsible for checking whether animal body parts come from species on the CITES list of endangered species. Officials can now use a small DNA barcoding kit linked to a computer database to identify a species. Suggest two advantages of using this method to identify a species.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[1] group of (morphologically) similar organisms ;
[1] that interbreed to produce fertile offspring;
[1] occupy same niche;
[1] AVP; e.g. detail of molecular similarity
[1] ref. to geographical isolation ;
[1] no, gene flow / interbreeding, between, A and B / populations;
[1] different, selection pressures / environmental conditions (for A and B populations);
[1] different mutations occur (in A and B populations);
[1] some mutations make individuals better adapted ;
[1] those individuals, survive / reproduce ;
[1] pass on advantageous alleles ;
[1] ref. to many generations ;
[1] reproductive isolation;
[1] allopatric speciation;
[1] DNA sample placed in well (at end of gel) ;
[1] ref. to electric field / current;
[1] (negatively charged) DNA attracted to, anode / positive electrode ;
[1] shorter fragments move further in unit time / ora;
[1] compare band position to identify cat species ;
[1] quicker test;
[1] cheaper/good for low income countries ;
[1] portable / no special lab needed / no need to send off sample to be tested;
[1] many sequences can be stored / ref. to bioinformatics;
[1] AVP; e.g. more successful prosecutions deters others form illegal trading / new enforcement measures available

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