9 Turn over 4 In cats, the gene for fur length is not located on the X chromosome. The allele for short fur (F) is dominant to the allele for long fur (f). The pedigree diagram shows the inheritance of fur length in a family of cats. 1 2 3 4 5 6 7 9 10 11 12 13 8 male, short fur female, short fur male, long fur female, long fur Key (a) Explain how one piece of evidence from the diagram shows that the allele for short fur is dominant to the allele for long fur. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (b) A gene for fur colour in cats is located on the X chromosome. The alleles for black fur (XB) and orange fur (Xo) are codominant. Tortoiseshell cats have areas of black and orange fur. (i) Give all the possible genotypes of a male, black cat with short fur. (1) .................................................................................................................................................................................................................................................................................... 10 (ii) Explain why all tortoiseshell cats are female. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (iii) In a genetic cross, a tortoiseshell cat with long fur was mated with an orange male cat, heterozygous for fur length. Deduce the probability of producing a tortoiseshell cat with long fur from this cross. Use a genetic diagram to support your answer. (4) (Total for Question 4 = 9 marks) 11 Turn over BLANK PAGE