O-LevelBiologyGenetics & Variation5090/21 · May/June 2017 · Q412 Marks

Fig. 4.1 shows a Bengal tiger. Fur colour in the Bengal tiger is controlled by a single gene. The dominant allele of the gene results in orange fur. A single change in this gene produces a recessive allele, which results in white fur in tigers with the homozygous recessive genotype. [Figure 4.1]

(a)(i)Define the term gene.[3]
(a)(ii)State the term used to describe a change in a gene.[1]
(b)Using the letters T (orange) and t (white) to represent the alleles that control fur colour, draw a labelled genetic diagram to show how two tigers with orange fur may give rise to offspring with white fur.[5]
(c)Bengal tigers have dark stripes on their fur. Suggest why each of the following is true for the pattern of dark stripes: it is not affected by whether the fur is orange or white it is unique to each individual[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[3] 4(a)(i) section of/made of/ piece of + DNA / chromosome; controls production of one protein; may be copied ; unit of inheritance / passed on to next generation;
[1] 4(a)(ii) mutation;
[5] 4(b) Tt + Tt; tt; t+t; tt offspring clearly indicated as white; 3 x labels on genetic diagram correct;
[1] 4(c) (unaffected by fur colour) (controlled by) different gene(s) ;
[2] 4(c) (unique to each individual) alleles; (as a result of) mutation(s); meiosis AW; different combinations (of alleles); reference to some may be homozygous / heterozygous ; reference to codominance ;

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.